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    Chapter 2.1 · The starting line · Report

    Birthweight and preterm birth

    Low birthweight was 7.4% of births in the least deprived tenth of counties and 9.7% in the most deprived, for births in 2018 to 2024 in counties of 100,000 or more residents.

    Author
    Vishal Singh
    Affiliation
    NYU Stern
    Published

    Every estimate of the chapter with its interval and every figure as a table, generated from the chapter's data files. Table n of this report is figure n of the chapter. The same report as Markdown: report.md.

    Identification

    Title
    Birthweight and preterm birth
    Label
    The starting line
    Chapter
    2.1 (Part II, Birth; An American life)
    Question
    How do the shares of babies born at low birthweight or preterm change with county deprivation, and how much of the racial gap remains at every level of deprivation?
    Dek
    Low birthweight was 7.4% of births in the least deprived tenth of counties and 9.7% in the most deprived, for births in 2018 to 2024 in counties of 100,000 or more residents.
    Grain
    counties
    Status
    published
    Published
    Updated
    not revised
    Data sources
    • CDC WONDER natality. CDC WONDER natality, county by birthweight and gestational age, births in 2018 to 2024; years: 2018-2024; weights: none (full counts of births); county shares weighted by births
    • Area Deprivation Index. Neighborhood Atlas Area Deprivation Index 2023 (v4.0.1), tract national rank, averaged to counties with 2019-2023 tract population; years: 2023 release (version 4.0.1; built on ACS 2019-2023); weights: 2019-2023 tract population
    • County Health Rankings. County Health Rankings 2024, low birthweight (births in 2016 to 2022), overall and for non-Hispanic Black, non-Hispanic white and Hispanic mothers; years: 2024 release; weights: births (recovered from published intervals for race groups)
    • CDC WONDER linked birth and infant death. CDC WONDER linked birth and infant death, mother's single race (any ethnicity), 2018 and 2019; years: 2018-2022; weights: none (crude rates from counts)
    Canonical URL
    https://vishalsingh.org/zipcode/birthweight-and-preterm-birth
    Markdown
    https://vishalsingh.org/zipcode/birthweight-and-preterm-birth/report.md
    BibTeX
    @misc{singh2026birthweightandpretermbirth,
  author = {Singh, Vishal},
  title = {Birthweight and preterm birth},
  year = {2026},
  url = {https://vishalsingh.org/zipcode/birthweight-and-preterm-birth},
  note = {In ZIP Code Destiny. Published 9 October 2026.}
}

    Principal estimates

    The facts the dek and the opening prose cite, in order of appearance. Every fact is in the table of all estimates below.

    EstimandPopulationPeriodValueIntervalnWeightsSourceFact id
    births-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the least deprived tenth of the named counties by county deprivation rankbirths in 2018 to 20247.4%95% CI 7.2% to 7.7%57 countiesbirths in each countyCDC WONDER natalitylbw_d1
    births-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the most deprived tenth of the named counties by county deprivation rankbirths in 2018 to 20249.7%95% CI 9.2% to 10.3%58 countiesbirths in each countyCDC WONDER natalitylbw_d10
    population size at which WONDER names a county (a definition)counties that CDC WONDER natality names individuallybirths in 2018 to 2024100,000none (definition)CDC WONDER natalitywonder_threshold
    birthweight below which a live birth counts as low birthweight (a definition)live birthsall years (a definition)2,500none (definition)CDC WONDER natalitylbw_cutoff_grams
    gestational age below which a live birth counts as preterm, obstetric estimate (a definition)live birthsall years (a definition)37none (definition)CDC WONDER natalitypreterm_cutoff_weeks
    births-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the least deprived tenth of the named counties by county deprivation rankbirths in 2018 to 20248.8%95% CI 8.6% to 9.0%57 countiesbirths in each countyCDC WONDER natalitypreterm_lo
    births-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the most deprived tenth of the named counties by county deprivation rankbirths in 2018 to 202412.1%95% CI 11.3% to 12.7%58 countiesbirths in each countyCDC WONDER natalitypreterm_hi
    count of countiescounties that WONDER natality names individually and that have birthsbirths in 2018 to 2024578none (full count)CDC WONDER natalitycounties_used
    share of births in the named countieslive births in the 50 states and DCbirths in 2018 to 202479.5%25,709,900 birthsnone (full count)CDC WONDER natalitybirths_share_covered
    pooled share of births, from the published county rates and the births they imply, bootstrap interval over countieslive births to non-Hispanic Black mothers in the named counties where County Health Rankings publishes the ratebirths in 2016 to 202214.0%95% CI 13.8% to 14.2%549 countiesbirths to mothers of the group in each countyCounty Health Rankingslbw_black
    pooled share of births, from the published county rates and the births they imply, bootstrap interval over countieslive births to non-Hispanic white mothers in the named counties where County Health Rankings publishes the ratebirths in 2016 to 20226.7%95% CI 6.6% to 6.8%578 countiesbirths to mothers of the group in each countyCounty Health Rankingslbw_white
    pooled share of births, bootstrap interval over countieslive births to non-Hispanic Black mothers in the least deprived quartile of the named counties by deprivation rankbirths in 2016 to 202212.4%95% CI 11.9% to 12.8%133 countiesbirths to mothers of the group in each countyCounty Health Rankingslbw_black_q1
    pooled share of births, bootstrap interval over countieslive births to non-Hispanic white mothers in the most deprived quartile of the named counties by deprivation rankbirths in 2016 to 20227.6%95% CI 7.5% to 7.7%145 countiesbirths to mothers of the group in each countyCounty Health Rankingslbw_white_q4

    Findings

    Low birthweightLow birthweightA live birth weighing less than 2,500 grams, the cutoff used in vital statistics., a weight under 2,5002,500 gramsEstimandbirthweight below which a live birth counts as low birthweight (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality grams, was 7.4%7.4% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 7.2% to 7.7%n57 countiesWeightsbirths in each countyPopulationlive births in the least deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births in the least deprived tenth of the counties that CDC WONDER names individually and 9.7%9.7% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 9.2% to 10.3%n58 countiesWeightsbirths in each countyPopulationlive births in the most deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality in the most deprived, for births in 2018 to 2024. Preterm birthPreterm birthA birth before 37 weeks of pregnancy., before 3737 completed weeks of gestationEstimandgestational age below which a live birth counts as preterm, obstetric estimate (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality weeks, was 8.8%8.8% percent of live births before 37 weeksEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 8.6% to 9.0%n57 countiesWeightsbirths in each countyPopulationlive births in the least deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality against 12.1%12.1% percent of live births before 37 weeksEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 11.3% to 12.7%n58 countiesWeightsbirths in each countyPopulationlive births in the most deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality. WONDER names only the larger counties, 578578 countiesEstimandcount of countiesWeightsnone (full count)Populationcounties that WONDER natality names individually and that have birthsPeriodbirths in 2018 to 2024SourceCDC WONDER natality of them. They hold 79.5%79.5% percent of live births in the United StatesEstimandshare of births in the named countiesn25,709,900 birthsWeightsnone (full count)Populationlive births in the 50 states and DCPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births in the United States, so the pattern covers most newborns, though not those in the smaller counties that WONDER pools.

    In County Health Rankings rates for births in 2016 to 2022, low birthweight was 14.0%14.0% percent of live births under 2,500 gramsEstimandpooled share of births, from the published county rates and the births they imply, bootstrap interval over countiesInterval95% CI 13.8% to 14.2%n549 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic Black mothers in the named counties where County Health Rankings publishes the ratePeriodbirths in 2016 to 2022SourceCounty Health Rankings of births to non-Hispanic Black mothers and 6.7%6.7% percent of live births under 2,500 gramsEstimandpooled share of births, from the published county rates and the births they imply, bootstrap interval over countiesInterval95% CI 6.6% to 6.8%n578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic white mothers in the named counties where County Health Rankings publishes the ratePeriodbirths in 2016 to 2022SourceCounty Health Rankings of births to non-Hispanic white mothers in these counties. The rate for non-Hispanic Black mothers is higher than the rate for non-Hispanic white mothers in every quartile of county deprivation. In the least deprived quartile of counties it is 12.4%12.4% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 11.9% to 12.8%n133 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic Black mothers in the least deprived quartile of the named counties by deprivation rankPeriodbirths in 2016 to 2022SourceCounty Health Rankings, higher than the rate for non-Hispanic white mothers in the most deprived quartile, 7.6%7.6% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 7.5% to 7.7%n145 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic white mothers in the most deprived quartile of the named counties by deprivation rankPeriodbirths in 2016 to 2022SourceCounty Health Rankings. The gap between the two groups is therefore not a difference between richer and poorer counties alone.

    Everything in this chapter describes counties and groups of births, not individual mothers. A county's deprivation rank says how disadvantaged its neighborhoods are on average, and a rate is the share of that county's births. Infant mortality, the outcome that follows these births, is the subject of Chapter 2.2, Infant mortality.

    Why the first two measurements matter

    Birthweight and gestational age are recorded on the birth certificate, which makes them the standard early measures of how a pregnancy went. A baby under 2,5002,500 gramsEstimandbirthweight below which a live birth counts as low birthweight (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality grams counts as low birthweight, and a baby born before 3737 completed weeks of gestationEstimandgestational age below which a live birth counts as preterm, obstetric estimate (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality weeks counts as preterm. In the counties WONDER names, 8.3%8.3% percent of live births under 2,500 gramsEstimandpooled share of births in published cells (events over births), Wilson intervalInterval95% CI 8.3% to 8.3%n20,406,425 birthsWeightsnone (full counts of births)Populationlive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more), births in published cellsPeriodbirths in 2018 to 2024SourceCDC WONDER natalityNoteWONDER withholds cells of 1 to 9 births; a withheld cell is left out of both the count and the denominator. of babies born in 2018 to 2024 were low birthweight and 10.1%10.1% percent of live births before 37 weeksEstimandpooled share of births in published cells (events over births), Wilson intervalInterval95% CI 10.1% to 10.1%n20,418,250 birthsWeightsnone (full counts of births)Populationlive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more), births in published cellsPeriodbirths in 2018 to 2024SourceCDC WONDER natality were preterm. The two overlap, since a baby born early is usually small, though a baby can also be small at full term. Across the large counties the two county shares move closely together, with a correlation of 0.840.84 correlation coefficientEstimandbirths-weighted correlation between the county low-birthweight share and the county preterm share, county-cluster bootstrap intervalInterval95% CI 0.81 to 0.87n578 countiesWeightsbirths in each countyPopulationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality.

    Economists and epidemiologists study these measures because they predict what comes later. The literature on the fetal origins of adult health links conditions in the womb to test scores, educational attainment and income as well as health in adulthood.[1] A review by Aizer and Currie reports that health at birth predicts education, income and disability. It also reports that a mother's disadvantage is associated with worse health at birth through her health behaviors, her exposure to environmental hazards, her access to medical care and her own health.[2] A gradient in birthweight across places therefore matters beyond the delivery room, although these data cannot show how much of any later outcome a baby's birthweight accounts for.

    Where low birthweight is most common

    Low birthweight is not spread evenly across the country. In County Health Rankings rates for births in 2016 to 2022, 89%89% percent of countiesEstimandshare of those counties in the Census South region (16 states and DC)n290 countiesWeightsnone (each county counts once)Populationmapped counties in the highest tenth of low-birthweight sharesPeriodbirths in 2016 to 2022SourceCounty Health Rankings of the counties in the highest tenth of rates are in the South, which holds 47%47% percent of countiesEstimandshare of mapped counties in the Census South region (16 states and DC)n2,900 countiesWeightsnone (each county counts once)Populationall mapped countiesPeriodbirths in 2016 to 2022SourceCounty Health Rankings of the mapped counties. Of the same highest tenth, 64%64% percent of countiesEstimandshare of those counties in Alabama, Georgia, Louisiana, Mississippi and South Carolinan290 countiesWeightsnone (each county counts once)Populationmapped counties in the highest tenth of low-birthweight sharesPeriodbirths in 2016 to 2022SourceCounty Health Rankings are in Alabama, Georgia, Louisiana, Mississippi and South Carolina, which hold 14%14% percent of countiesEstimandshare of mapped counties in Alabama, Georgia, Louisiana, Mississippi and South Carolinan2,900 countiesWeightsnone (each county counts once)Populationall mapped countiesPeriodbirths in 2016 to 2022SourceCounty Health Rankings. Pooled over births, the rate is 9.1%9.1% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 9.0% to 9.3%n1,371 countiesWeightsbirths in each county (CHR denominator)Populationlive births in mapped counties in the Census South region (16 states and DC)Periodbirths in 2016 to 2022SourceCounty Health Rankings in the South and 7.8%7.8% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 7.7% to 8.0%n1,529 countiesWeightsbirths in each county (CHR denominator)Populationlive births in mapped counties outside the Census South regionPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the rest of the country.

    Table 1. Low birthweight is most common in the South, where 89% of the counties in the highest tenth of shares lie, against 47% of mapped counties

    The map draws every county with at least 2020 low-birthweight birthsEstimandfewest low-birthweight births for which a county is drawn (a floor set for this book)Weightsnone (definition)Populationcounties on the mapPeriodbirths in 2016 to 2022SourceCounty Health Rankings low-birthweight births in the period, 2,9002,900 countiesEstimandcount of counties with a rate and at least 20 low-birthweight birthsWeightsnone (full count)Populationcounties and county equivalents on the map (50 states and DC)Periodbirths in 2016 to 2022SourceCounty Health Rankings counties in all. The other 243243 countiesEstimandcount of counties with no rate or fewer than 20 low-birthweight birthsWeightsnone (full count)Populationcounties and county equivalents on the map (50 states and DC)Periodbirths in 2016 to 2022SourceCounty Health Rankings counties are gray, and the tooltip gives the reason for each: 9898 countiesEstimandcount of counties for which County Health Rankings publishes no low-birthweight rateWeightsnone (full count)Populationcounties and county equivalents on the map (50 states and DC)Periodbirths in 2016 to 2022SourceCounty Health Rankings have no published rate and 145145 countiesEstimandcount of counties with a rate but fewer than 20 low-birthweight births, which the map leaves as no dataWeightsnone (full count)Populationcounties and county equivalents on the map (50 states and DC)Periodbirths in 2016 to 2022SourceCounty Health Rankings fall below the floor. County Health Rankings is a second source for this chapter. It takes its birth counts from the same national vital statistics system as WONDER, although the periods overlap only in 2018 to 2022 (WONDER 2018 to 2024, County Health Rankings 2016 to 2022). Where both cover a county they agree. Across the large counties the correlation between the two county shares is 0.9840.984 correlation coefficientEstimandbirths-weighted correlation between the county low-birthweight share in WONDER and in County Health Rankings, county-cluster bootstrap intervalInterval95% CI 0.980 to 0.987n578 countiesWeightsWONDER births in each countyPopulationthe named countiesPeriodWONDER births in 2018 to 2024 and CHR births in 2016 to 2022SourceCounty Health Rankings. That agreement lets the chapter use WONDER for the deprivation gradient and County Health Rankings for the map and for rates by mother's race and ethnicity, which the WONDER county files used here do not carry.

    Low birthweight and preterm birth rise with county deprivation

    To place counties on one scale, each census tract carries its Area Deprivation IndexArea Deprivation Index (ADI)A score that ranks neighborhoods by income, education, employment and housing conditions drawn from the American Community Survey. In this book a higher national percentile means a more deprived neighborhood. national rank, which orders the country's neighborhoods by deprivation using income, education, employment and housing measures from the American Community Survey.[3] A higher rank means more deprived. A county's rank in this chapter is the average of its tracts' ranks, weighting each tract by its population. The counties in the gradient are the 578578 countiesEstimandcount of countiesWeightsnone (full count)Populationcounties that WONDER natality names individually and that have birthsPeriodbirths in 2018 to 2024SourceCDC WONDER natality that WONDER natality names individually, those with 100,000100,000 residentsEstimandpopulation size at which WONDER names a county (a definition)Weightsnone (definition)Populationcounties that CDC WONDER natality names individuallyPeriodbirths in 2018 to 2024SourceCDC WONDER natality or more residents. WONDER pools the births of every other county in a state into one row labeled Unidentified Counties, so smaller counties cannot be separated. The named counties hold 20.5 million20.5 million live birthsEstimandcount of live birthsn20,450,654 birthsWeightsnone (full count)Populationlive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more)Periodbirths in 2018 to 2024SourceCDC WONDER natality births in 2018 to 2024. A tenth of counties here is a tenth of these large counties, so the most deprived tenth is relative to large counties and not to the nation.

    Low birthweight rises at every step from the least deprived tenth, 7.4% (95% CI 7.2% to 7.7%)7.4% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 7.2% to 7.7%n57 countiesWeightsbirths in each countyPopulationlive births in the least deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality, to the most deprived, 9.7% (95% CI 9.2% to 10.3%)9.7% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 9.2% to 10.3%n58 countiesWeightsbirths in each countyPopulationlive births in the most deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality, a difference of 2.3 percentage points (95% CI 1.7 percentage points to 2.9 percentage points)2.3 percentage points percentage pointsEstimanddifference of two births-weighted decile means of the low-birthweight share, bootstrap interval over countiesInterval95% CI 1.7 percentage points to 2.9 percentage pointsn578 countiesWeightsbirths in each countyPopulationlive births in the named counties, most deprived tenth minus least deprived tenthPeriodbirths in 2018 to 2024SourceCDC WONDER natality. Preterm birth follows the same path, from 8.8%8.8% percent of live births before 37 weeksEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 8.6% to 9.0%n57 countiesWeightsbirths in each countyPopulationlive births in the least deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality to 12.1%12.1% percent of live births before 37 weeksEstimandbirths-weighted mean of county shares (the pooled share), bootstrap interval over countiesInterval95% CI 11.3% to 12.7%n58 countiesWeightsbirths in each countyPopulationlive births in the most deprived tenth of the named counties by county deprivation rankPeriodbirths in 2018 to 2024SourceCDC WONDER natality, a larger difference of 3.2 percentage points (95% CI 2.5 percentage points to 3.9 percentage points)3.2 percentage points percentage pointsEstimanddifference of two births-weighted decile means of the preterm share, bootstrap interval over countiesInterval95% CI 2.5 percentage points to 3.9 percentage pointsn578 countiesWeightsbirths in each countyPopulationlive births in the named counties, most deprived tenth minus least deprived tenthPeriodbirths in 2018 to 2024SourceCDC WONDER natality computed from the unrounded shares.

    Across all 578578 countiesEstimandcount of countiesWeightsnone (full count)Populationcounties that WONDER natality names individually and that have birthsPeriodbirths in 2018 to 2024SourceCDC WONDER natality counties the low-birthweight share moves with the deprivation rank. It is higher by 0.38 percentage points (95% CI 0.32 percentage points to 0.44 percentage points)0.38 percentage points percentage points of the low-birthweight share per ten points of county deprivation rankEstimandbirths-weighted slope of the county low-birthweight share on county deprivation rank, county-cluster bootstrap intervalInterval95% CI 0.32 percentage points to 0.44 percentage pointsn578 countiesWeightsbirths in each countyPopulationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality for each ten-point step in the rank, and the correlation is 0.520.52 correlation coefficientEstimandbirths-weighted correlation of the county low-birthweight share with county deprivation rank, county-cluster bootstrap intervalInterval95% CI 0.45 to 0.58n578 countiesWeightsbirths in each countyPopulationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality. The preterm share is higher by 0.49 percentage points0.49 percentage points percentage points of the preterm share per ten points of county deprivation rankEstimandbirths-weighted slope of the county preterm share on county deprivation rank, county-cluster bootstrap intervalInterval95% CI 0.44 percentage points to 0.55 percentage pointsn578 countiesWeightsbirths in each countyPopulationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality for each ten-point step in the rank, with a correlation of 0.690.69 correlation coefficientEstimandbirths-weighted correlation of the county preterm share with county deprivation rank, county-cluster bootstrap intervalInterval95% CI 0.64 to 0.73n578 countiesWeightsbirths in each countyPopulationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality. The intervals are wider in the most deprived tenth than in the least deprived one, because the most deprived tenth holds fewer births and its counties' shares vary more. Averaging the counties without weighting by births gives the same ordering.

    Table 2. Low birthweight rises from 7.4% of births in the least deprived tenth of large counties to 9.7% in the most deprived

    Restricting the gradient to large counties could change the picture, so County Health Rankings offers a check. It publishes low-birthweight rates for 3,0403,040 countiesEstimandcount of countiesWeightsnone (full count)Populationcounties with a County Health Rankings low-birthweight rate and an ADIPeriodbirths in 2016 to 2022SourceCounty Health Rankings counties that also have a deprivation rank. In tenths of all those counties the share is 7.6%7.6% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares, bootstrap interval over countiesInterval95% CI 7.4% to 7.8%n304 countiesWeightsbirths in each county (CHR denominator)Populationlive births in the least deprived tenth of all counties with a County Health Rankings rate and an ADIPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the least deprived tenth and 10.9%10.9% percent of live births under 2,500 gramsEstimandbirths-weighted mean of county shares, bootstrap interval over countiesInterval95% CI 10.6% to 11.3%n304 countiesWeightsbirths in each county (CHR denominator)Populationlive births in the most deprived tenth of all counties with a County Health Rankings rate and an ADIPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the most deprived. The middle tenths are level, so the climb is steadier across large counties than across the whole country. The most deprived tenth of all counties is made up of small counties: its median county has 770770 live birthsEstimandmedian of the county birth counts behind the rate (CHR denominator)n304 countiesWeightsnone (each county counts once)Populationthe median county in the most deprived tenth of all counties with a County Health Rankings rate and an ADIPeriodbirths in 2016 to 2022SourceCounty Health Rankings births in the period, against 12,05512,055 live birthsEstimandmedian of the county birth counts behind the rate (CHR denominator)n304 countiesWeightsnone (each county counts once)Populationthe median county in the least deprived tenth of all counties with a County Health Rankings rate and an ADIPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the least deprived tenth, and its interval is wider.

    WONDER withholds any cell with fewer than 1010 birthsEstimanda cell with fewer births than this is withheld (a definition)Weightsnone (definition)Populationcells of the WONDER natality filesPeriodbirths in 2018 to 2024SourceCDC WONDER natality births, so a county's count below 2,5002,500 gramsEstimandbirthweight below which a live birth counts as low birthweight (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality grams is not always published whole. A withheldSuppressionThe withholding of a number because the count behind it is too small to publish without risking the identification of a person. A suppressed value is missing, not zero. cell is treated as missing: it is left out of both the count and the denominator, which is the births in the published cells. The birthweight cut has 11,25011,250 withheld cellsEstimandcount of cells with 1 to 9 births, which WONDER withholdsWeightsnone (full count)Populationcounty-year cells of the WONDER birthweight cut in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality withheld cells in these counties. Because each holds fewer than 1010 birthsEstimanda cell with fewer births than this is withheld (a definition)Weightsnone (definition)Populationcells of the WONDER natality filesPeriodbirths in 2018 to 2024SourceCDC WONDER natality births, together they could hold at most 0.5%0.5% percent of live birthsEstimandlargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in the countiesWeightsnone (an upper limit from the cell count)Populationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births. The gestational-age cut has 8,7048,704 withheld cellsEstimandcount of cells with 1 to 9 births, which WONDER withholdsWeightsnone (full count)Populationcounty-year cells of the WONDER gestational-age cut in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality withheld cells, which could hold at most 0.4%0.4% percent of live birthsEstimandlargest share of births the withheld gestational-age cells could hold: 9 births in each withheld cell, over all births in the countiesWeightsnone (an upper limit from the cell count)Populationlive births in the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births. A pooled share could therefore move by no more than that amount.

    The withheld cells are not spread evenly. Withheld cells under 2,5002,500 gramsEstimandbirthweight below which a live birth counts as low birthweight (a definition)Weightsnone (definition)Populationlive birthsPeriodall years (a definition)SourceCDC WONDER natality grams number 1.61.6 withheld cells per county-yearEstimandwithheld birthweight cells below the low-birthweight cutoff, per county-yearn406 county-yearsWeightsnone (full count)Populationcounty-years of the most deprived tenth of the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality per county-year in the most deprived tenth against 1.01.0 withheld cells per county-yearEstimandwithheld birthweight cells below the low-birthweight cutoff, per county-yearn399 county-yearsWeightsnone (full count)Populationcounty-years of the least deprived tenth of the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality in the least deprived. A withheld cell of that kind lowers a published share, because its births leave the count and the denominator together. With fewer than 1010 birthsEstimanda cell with fewer births than this is withheld (a definition)Weightsnone (definition)Populationcells of the WONDER natality filesPeriodbirths in 2018 to 2024SourceCDC WONDER natality births in each, the withheld birthweight cells could hold at most 1.3%1.3% percent of live birthsEstimandlargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in these countiesWeightsnone (an upper limit from the cell count)Populationlive births in the most deprived tenth of the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births in the most deprived tenth and 0.2%0.2% percent of live birthsEstimandlargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in these countiesWeightsnone (an upper limit from the cell count)Populationlive births in the least deprived tenth of the named countiesPeriodbirths in 2018 to 2024SourceCDC WONDER natality in the least deprived. The published difference between the tenths could therefore be too small by up to the first amount, and too large by up to the second.

    The gap by mother's race

    The gradient averages over mothers. Splitting births by the mother's race and ethnicity shows a gap larger than the one between the most and least deprived counties. County Health Rankings counts mothers as non-Hispanic Black, non-Hispanic white or Hispanic of any race. In the large counties, 14.0%14.0% percent of live births under 2,500 gramsEstimandpooled share of births, from the published county rates and the births they imply, bootstrap interval over countiesInterval95% CI 13.8% to 14.2%n549 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic Black mothers in the named counties where County Health Rankings publishes the ratePeriodbirths in 2016 to 2022SourceCounty Health Rankings of births to non-Hispanic Black mothers in 2016 to 2022 were low birthweight, against 7.5%7.5% percent of live births under 2,500 gramsEstimandpooled share of births, from the published county rates and the births they imply, bootstrap interval over countiesInterval95% CI 7.4% to 7.7%n575 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to Hispanic (any race) mothers in the named counties where County Health Rankings publishes the ratePeriodbirths in 2016 to 2022SourceCounty Health Rankings for Hispanic mothers and 6.7%6.7% percent of live births under 2,500 gramsEstimandpooled share of births, from the published county rates and the births they imply, bootstrap interval over countiesInterval95% CI 6.6% to 6.8%n578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic white mothers in the named counties where County Health Rankings publishes the ratePeriodbirths in 2016 to 2022SourceCounty Health Rankings for non-Hispanic white mothers. The rate for non-Hispanic Black mothers is 2.1 (95% CI 2.0 to 2.1)2.1 ratio of ratesEstimandratio of pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 2.0 to 2.1n578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the named counties, non-Hispanic Black mothers over non-Hispanic white mothersPeriodbirths in 2016 to 2022SourceCounty Health Rankings times the rate for non-Hispanic white mothers, a gap of 7.3 percentage points (95% CI 7.0 percentage points to 7.4 percentage points)7.3 percentage points percentage pointsEstimanddifference of pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 7.0 percentage points to 7.4 percentage pointsn578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersPeriodbirths in 2016 to 2022SourceCounty Health Rankings. The difference between the most and least deprived tenths of counties was 2.3 percentage points2.3 percentage points percentage pointsEstimanddifference of two births-weighted decile means of the low-birthweight share, bootstrap interval over countiesInterval95% CI 1.7 percentage points to 2.9 percentage pointsn578 countiesWeightsbirths in each countyPopulationlive births in the named counties, most deprived tenth minus least deprived tenthPeriodbirths in 2018 to 2024SourceCDC WONDER natality, for births in 2018 to 2024.

    Infant deaths follow the same order. WONDER's linked birth and infant death records report mother's race only for 2018 and 2019, as a single race of any ethnicity. They give 10.3 deaths per 1,000 live births10.3 deaths per 1,000 live births infant deaths per 1,000 live birthsEstimandcrude rate from state counts, normal intervalInterval95% CI 10.10 to 10.50n12,953 infant deathsWeightsnone (crude rate from counts)Populationlive births to Black mothers (single race, any ethnicity) in the United States, states with a published countPeriodbirths in 2018 and 2019SourceCDC WONDER linked birth and infant death for births to Black mothers against 4.74.7 infant deaths per 1,000 live birthsEstimandcrude rate from state counts, normal intervalInterval95% CI 4.7 to 4.8n26,516 infant deathsWeightsnone (crude rate from counts)Populationlive births to white mothers (single race, any ethnicity) in the United States, states with a published countPeriodbirths in 2018 and 2019SourceCDC WONDER linked birth and infant death for births to white mothers, a group that includes Hispanic mothers.

    Table 3. Non-Hispanic Black mothers had low-birthweight births at 14.0% against 6.7% for non-Hispanic white mothers, a ratio of 2.1

    These are rates for groups of births in counties and say nothing about why a given mother's baby is born small. One study that bears on the explanation compared infants born in Illinois from 1980 to 1995. Infants of African-born Black mothers were heavier on average than infants of U.S.-born Black mothers and closer in weight to infants of U.S.-born white mothers.[4] That pattern is hard to square with an explanation based on ancestry alone. Women who migrate are a selected group, though, so the comparison cannot rule out other differences between the two groups of Black mothers.

    The gap at every level of deprivation

    Counties differ in deprivation, so the race gap could shrink once counties are compared at the same level. In every quartile of county deprivation, the rate for non-Hispanic Black mothers is higher than the rate for non-Hispanic white mothers, for births in 2016 to 2022 (Table 4). The gap is 6.2 percentage points (95% CI 5.8 percentage points to 6.6 percentage points)6.2 percentage points percentage pointsEstimanddifference of pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 5.8 percentage points to 6.6 percentage pointsn578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the least deprived quartile of the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the least deprived quartile and 8.0 percentage points (95% CI 7.7 percentage points to 8.2 percentage points)8.0 percentage points percentage pointsEstimanddifference of pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 7.7 percentage points to 8.2 percentage pointsn578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the most deprived quartile of the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersPeriodbirths in 2016 to 2022SourceCounty Health Rankings in the most deprived, and the second is larger than the first by 1.8 percentage points (95% CI 1.3 percentage points to 2.3 percentage points)1.8 percentage points percentage pointsEstimanddifference of two Black-white gaps in pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 1.3 percentage points to 2.3 percentage pointsn578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the named counties, gap between non-Hispanic Black and non-Hispanic white mothers in the most deprived quartile minus the gap in the least deprived quartilePeriodbirths in 2016 to 2022SourceCounty Health Rankings. The rate for non-Hispanic Black mothers in the least deprived quartile, 12.4% (95% CI 11.9% to 12.8%)12.4% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 11.9% to 12.8%n133 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic Black mothers in the least deprived quartile of the named counties by deprivation rankPeriodbirths in 2016 to 2022SourceCounty Health Rankings, is higher than the rate for non-Hispanic white mothers in the most deprived quartile, 7.6% (95% CI 7.5% to 7.7%)7.6% percent of live births under 2,500 gramsEstimandpooled share of births, bootstrap interval over countiesInterval95% CI 7.5% to 7.7%n145 countiesWeightsbirths to mothers of the group in each countyPopulationlive births to non-Hispanic white mothers in the most deprived quartile of the named counties by deprivation rankPeriodbirths in 2016 to 2022SourceCounty Health Rankings, by 4.8 percentage points (95% CI 4.4 percentage points to 5.2 percentage points)4.8 percentage points percentage pointsEstimanddifference of two pooled low-birthweight shares, county-cluster bootstrap intervalInterval95% CI 4.4 percentage points to 5.2 percentage pointsn578 countiesWeightsbirths to mothers of the group in each countyPopulationlive births in the named counties: non-Hispanic Black mothers in the least deprived quartile minus non-Hispanic white mothers in the most deprived quartilePeriodbirths in 2016 to 2022SourceCounty Health Rankings. The second view of the figure shows the same order for infant mortality, with Black and white mothers counted by single race of any ethnicity, in counties of 250,000250,000 residentsEstimandpopulation size at which WONDER names a county in the linked file (a definition)Weightsnone (definition)Populationcounties that CDC WONDER linked birth and infant death names individuallyPeriodbirths in 2018 and 2019SourceCDC WONDER linked birth and infant death residents or more, for births in 2018 and 2019.

    Table 4. Low birthweight is more common for non-Hispanic Black mothers in the least deprived quartile of counties (12.4%) than for non-Hispanic white mothers in the most deprived (7.6%)

    The weatheringWeatheringThe hypothesis that chronic stress from disadvantage and discrimination wears down health faster, so that the same outcomes appear at younger ages in affected groups. Arline Geronimus proposed it in studies of birth outcomes. hypothesis proposed by Geronimus holds that the health of Black women may begin to deteriorate in early adulthood as a physical consequence of cumulative socioeconomic disadvantage.[5] A gap that persists at every level of county deprivation is consistent with it, but a comparison across counties cannot separate it from other explanations.

    A county's rank averages over neighborhoods that differ a great deal. A Black mother in a county ranked among the least deprived may live in a neighborhood more deprived than the county average. A white mother in a county ranked among the most deprived may live in a less deprived one. The comparison therefore cannot show that mothers under the same neighborhood conditions have different outcomes. What it shows is that sorting counties by deprivation does not remove the gap. A comparison of Black and white children raised in the same tract is in Chapter 4.3, Race, income and mobility.

    Births fell between 2018 and 2024

    Births in the United States fell from 3.79 million3.79 million live birthsEstimandcount of live birthsWeightsnone (full count)Populationlive births in the United StatesPeriod2018SourceCDC WONDER natality in 2018 to 3.63 million3.63 million live birthsEstimandcount of live birthsWeightsnone (full count)Populationlive births in the United StatesPeriod2024SourceCDC WONDER natality in 2024, a decline of 4.3%4.3% percent of 2018 birthsEstimandfall in the count of births from 2018 to 2024Weightsnone (full count)Populationlive births in the United StatesPeriod2018 to 2024SourceCDC WONDER natality. The shares in this chapter are rates, so they do not move with the count, but the pattern describes a smaller number of babies each year. Where the decline is steepest is the subject of Chapter 2.4, Where births are falling.

    Two studies of income and insurance during pregnancy

    The gradient and the gap are descriptions. Two studies of policy changes give evidence on whether income support and insurance coverage during pregnancy change birthweight, and each is reported under its own design.

    Both sets of estimates apply to the policies and years studied. They do not measure how much of the county gradient or the race gap those policies would close.

    Low birthweight keeps its gradient under the standardized index and flattens under the degree share

    Table 5 ranks the 578578 countiesEstimandcount of counties in the common sample of the ranking comparisonWeightsnone (full count)Populationcounties with the outcome and all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality large counties that have all four rankings in four ways. Ranked by the ADI on this common sample, the low-birthweight share of births is 7.4% (95% CI 7.2% to 7.7%)7.4% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 7.2% to 7.7%n57 countiesWeightsbirths in each countyPopulationthe least deprived tenth of counties ranked by Area Deprivation Index, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality in the least deprived tenth and 9.6% (95% CI 9.1% to 10.2%)9.6% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 9.1% to 10.2%n58 countiesWeightsbirths in each countyPopulationthe most deprived tenth of counties ranked by Area Deprivation Index, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality in the most deprived, and the rank correlation between tenth and share is +0.99+0.99 rank correlationEstimandSpearman rank correlation between bin order and bin mean, each bin counted onceWeightseach bin counted oncePopulationthe bins of counties ranked by Area Deprivation IndexPeriodbirths in 2018 to 2024SourceCDC WONDER natality. Under the standardized index the two ends are 7.2% (95% CI 7.0% to 7.3%)7.2% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 7.0% to 7.3%n57 countiesWeightsbirths in each countyPopulationthe least deprived tenth of counties ranked by Standardized index, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality and 9.7% (95% CI 9.0% to 10.4%)9.7% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 9.0% to 10.4%n58 countiesWeightsbirths in each countyPopulationthe most deprived tenth of counties ranked by Standardized index, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality, with a correlation of +0.99+0.99 rank correlationEstimandSpearman rank correlation between bin order and bin mean, each bin counted onceWeightseach bin counted oncePopulationthe bins of counties ranked by Standardized indexPeriodbirths in 2018 to 2024SourceCDC WONDER natality, and under median household income they are 7.2% (95% CI 7.0% to 7.3%)7.2% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 7.0% to 7.3%n57 countiesWeightsbirths in each countyPopulationthe least deprived tenth of counties ranked by Median household income, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality and 10.0% (95% CI 9.4% to 10.6%)10.0% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 9.4% to 10.6%n58 countiesWeightsbirths in each countyPopulationthe most deprived tenth of counties ranked by Median household income, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality, with a correlation of +0.96+0.96 rank correlationEstimandSpearman rank correlation between bin order and bin mean, each bin counted onceWeightseach bin counted oncePopulationthe bins of counties ranked by Median household incomePeriodbirths in 2018 to 2024SourceCDC WONDER natality, so neither counts as a change under the book's rule (Chapter 9.1, How far one ranking goes). Ranked by the bachelor's degree share, the ends are 7.6% (95% CI 7.2% to 7.9%)7.6% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 7.2% to 7.9%n57 countiesWeightsbirths in each countyPopulationthe least deprived tenth of counties ranked by Bachelor's degree share, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality and 8.2% (95% CI 7.8% to 8.6%)8.2% Births under 2,500 grams (% of live births)Estimandbirths-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesInterval95% CI 7.8% to 8.6%n58 countiesWeightsbirths in each countyPopulationthe most deprived tenth of counties ranked by Bachelor's degree share, among the counties with all four rankingsPeriodbirths in 2018 to 2024SourceCDC WONDER natality and their intervals overlap, which the rule counts as a change, although income and degree share are checks that cannot switch the book's ranking on their own.

    Table 5. Low birthweight is steadily worse toward the more deprived end under the ADI; the two ends do not differ detectably under the degree-share ranking

    What these data cannot show

    The county figures describe places, and a county rate is an average over the births in it. A county ranked as least deprived can hold deprived neighborhoods, and the Area Deprivation Index understates deprivation in high-cost cities (Chapter 1.1, What the deprivation index measures). A pattern across counties does not describe the babies in any one of them.

    The WONDER figures cover only counties of 100,000100,000 residentsEstimandpopulation size at which WONDER names a county (a definition)Weightsnone (definition)Populationcounties that CDC WONDER natality names individuallyPeriodbirths in 2018 to 2024SourceCDC WONDER natality or more residents, which hold 79.5%79.5% percent of live births in the United StatesEstimandshare of births in the named countiesn25,709,900 birthsWeightsnone (full count)Populationlive births in the 50 states and DCPeriodbirths in 2018 to 2024SourceCDC WONDER natality of births. Births in smaller counties are pooled by WONDER and cannot be placed on the deprivation scale, and the check against County Health Rankings shows that the pattern is less regular across all counties than across large ones.

    The sources differ in period and definition. The deprivation index draws on the American Community Survey for 2019 to 2023, while the births span 2018 to 2024. Rates by mother's race come from County Health Rankings for births in 2016 to 2022, for non-Hispanic Black, non-Hispanic white and Hispanic mothers, and they are pooled over the counties where a rate is published. Infant mortality by mother's race comes from 2018 and 2019 only, for single races of any ethnicity, so its white group includes Hispanic mothers and is not the group in the low-birthweight rates. The infant mortality county view covers only larger counties and leaves out county-years in which WONDER withholds the deaths, which are 13.6%13.6% percent of live birthsEstimandshare of births in county-years whose deaths WONDER withholds, which the county view leaves out of deaths and birthsWeightsnone (full counts of births)Populationlive births to black mothers (single race, any ethnicity) in counties of 250,000 residents or morePeriodbirths in 2018 and 2019SourceCDC WONDER linked birth and infant death of Black births and 5.2%5.2% percent of live birthsEstimandshare of births in county-years whose deaths WONDER withholds, which the county view leaves out of deaths and birthsWeightsnone (full counts of births)Populationlive births to white mothers (single race, any ethnicity) in counties of 250,000 residents or morePeriodbirths in 2018 and 2019SourceCDC WONDER linked birth and infant death of white births there. The intervals leave out those differences in source, period and group.

    Finally, none of these comparisons identifies a mechanism. Deprivation and race are tied to smoking, prenatal care, chronic stress, pollution, maternal age and education, and to the quality of the nearest hospital. Birthweight is associated with all of them. The two policy studies above are the only evidence in this chapter on what changes the numbers, and they speak to income and coverage, not to the rest. A county map cannot settle the mechanism behind any one county's rate or behind the gap between groups.

    Tables

    Table 1. Low birthweight is most common in the South, where 89% of the counties in the highest tenth of shares lie, against 47% of mapped counties

    Share of live births under 2,500 grams by county, County Health Rankings 2024, births in 2016 to 2022

    No inline rows: the values of Table 1 are in /data/birthweight-and-preterm-birth/lbw_map.json.

    Note: Counties with fewer than 10 low-birthweight births in the period have no rate in County Health Rankings, and counties with fewer than 20 are drawn as no data here, the same floor the book uses for death maps. 243 counties are not mapped.

    Note: The South is the Census South region (16 states and DC). County Health Rankings rates come from the same NCHS birth records as WONDER; across the large counties the two sources correlate at 0.984.

    Note: Connecticut is shown as its eight legacy counties, the coding of the source. Alaska is drawn. Puerto Rico is not drawn.

    Source: County Health Rankings 2024, births in 2016-2022 (NCHS natality counts); county rates, population-weighted by births

    Data: vishalsingh.org/zipcode/report/birthweight-and-preterm-birth/figures/lbw_map.json

    Table 2. Low birthweight rises from 7.4% of births in the least deprived tenth of large counties to 9.7% in the most deprived

    Share of live births under 2,500 grams (and before 37 weeks in the second tab) by county deprivation, 2018 to 2024

    Table 2.1. Low birthweight, large counties

    Across 578 large counties the low-birthweight share moves with the deprivation rank, a correlation of 0.52

    Share of live births under 2,500 grams against the county deprivation rank, one dot per county, 2018 to 2024, with births-weighted decile means

    adibirthscountylbw
    27.2735153Ada County, ID6.35
    31.5043865Adams County, CO9.34
    53.026346Adams County, PA5.23
    67.2113354Aiken County, SC9.03
    57.2718344Alachua County, FL10.40
    65.5713473Alamance County, NC9.47
    7.82119533Alameda County, CA7.49
    52.0919652Albany County, NY8.64
    18.6716409Alexandria city, VA6.56
    57.158760Allegan County, MI5.82
    60.0685018Allegheny County, PA8.94
    67.8536535Allen County, IN9.01
    77.548561Allen County, OH8.92
    37.2325918Anchorage Borough, AK6.89
    66.5115986Anderson County, SC9.33
    61.558066Androscoggin County, ME8.12
    26.3147568Anne Arundel County, MD7.57
    41.1128547Anoka County, MN6.93
    25.2552722Arapahoe County, CO10.10
    11.9617788Arlington County, VA6.18
    49.7111589Ascension Parish, LA9.58
    80.507231Ashtabula County, OH6.37
    54.0619373Atlantic County, NJ7.89
    50.2017176Baldwin County, AL7.93
    42.2865464Baltimore County, MD9.32
    64.9450993Baltimore city, MD12.02
    20.7810379Barnstable County, MA5.43
    54.239308Bartow County, GA6.77
    55.8514687Bay County, FL8.26
    80.216392Bay County, MI7.58
    37.1313141Beaufort County, SC8.11
    69.4510623Beaver County, PA6.79
    64.5742199Bell County, TX9.12
    48.2226503Benton County, AR7.35
    40.9817730Benton County, WA6.27
    19.4263171Bergen County, NJ7.44
    50.8020807Berkeley County, SC9.31
    54.8210636Berkeley County, WV8.17
    60.0931836Berks County, PA7.92
    49.996398Berkshire County, MA7.68
    54.4446209Bernalillo County, NM9.73
    66.5310686Berrien County, MI8
    59.17183350Bexar County, TX8.83
    75.8014382Bibb County, GA13.54
    69.5511194Black Hawk County, IA8.05
    76.458120Blair County, PA6.09
    53.459120Blount County, TN7.61
    4612633Bonneville County, ID7.81
    49.9711867Boone County, KY6.60
    58.4313758Boone County, MO8.40
    66.3611338Bossier Parish, LA11.42
    15.9417248Boulder County, CO7.77
    49.4332862Brazoria County, TX8.32
    55.9718815Brazos County, TX8.09
    48.9036470Brevard County, FL8.41
    34.0239240Bristol County, MA8.48
    31.09124256Bronx County, NY10.45
    78.3912584Broome County, NY7.98
    40.97145472Broward County, FL9.63
    56.9021131Brown County, WI7.06
    48.227781Brunswick County, NC7.76
    29.7139164Bucks County, PA6.99
    42.5016802Buncombe County, NC8.30
    40.1031808Burlington County, NJ7.72
    58.3330299Butler County, OH8
    50.2812033Butler County, PA5.92
    38.1314612Butte County, CA6.20
    46.2018406Cabarrus County, NC8.82
    37.5514438Cache County, UT5.83
    76.4120103Caddo Parish, LA14.52
    66.0518828Calcasieu Parish, LA10.55
    80.939096Calhoun County, AL8.77
    77.3510306Calhoun County, MI8.76
    84.108283Cambria County, PA8.21
    54.4742450Camden County, NJ9.05
    84.0541975Cameron County, TX8.51
    57.5213874Canadian County, OK6.76
    42.3922809Canyon County, ID6.65
    60.2611132Carroll County, GA8.14
    29.6611977Carroll County, MD5.58
    49.0916894Cass County, ND6.99
    64.8511691Catawba County, NC8.15
    44.548004Cecil County, MD7.08
    46.227675Centre County, PA4.55
    66.5014484Champaign County, IL8.81
    3012676Charles County, MD9.27
    35.0434737Charleston County, SC9.36
    51.127422Charlotte County, FL7.89
    56.2025303Chatham County, GA11.15
    83.818651Chautauqua County, NY7.72
    33.2219655Cherokee County, GA6.77
    39.9219793Chesapeake city, VA9.07
    26.6838149Chester County, PA6.19
    40.9128155Chesterfield County, VA7.96
    31.509595Chittenden County, VT5.44
    66.627253Citrus County, FL7.34
    21.1026316Clackamas County, OR5.97
    64.2110055Clark County, IN7.84
    39.24176293Clark County, NV9.37
    77.6511089Clark County, OH8.89
    26.6438736Clark County, WA6.67
    53.229286Clarke County, GA9.88
    49.9315614Clay County, FL8.42
    52.1220890Clay County, MO7.43
    71.4424539Clayton County, GA13.52
    55.4315577Clermont County, OH7.38
    59.9719200Cleveland County, OK7.63
    37.3861759Cobb County, GA8.82
    71.068859Cochise County, AZ7.32
    40.849348Coconino County, AZ6.95
    30.3123129Collier County, FL7.14
    26.5585845Collin County, TX7.47
    48.0311898Columbia County, GA7.21
    80.836778Columbiana County, OH7.32
    35.1212791Comal County, TX6.84
    77.5111401Comanche County, OK7.63
    12.7181039Contra Costa County, CA7.34
    47.08384972Cook County, IL8.94
    43.7811498Coweta County, GA9.35
    41.548603Cowlitz County, WA5.87
    66.659031Craven County, NC8.23
    30.7319393Cumberland County, ME6.76
    72.5336672Cumberland County, NC10.35
    68.2012811Cumberland County, NJ9.47
    53.1518447Cumberland County, PA6.79
    69.3392117Cuyahoga County, OH10.62
    35.8434751Dakota County, MN6.78
    51.84258092Dallas County, TX8.49
    37.4439430Dane County, WI7.16
    62.8823065Dauphin County, PA9.31
    68.3912395Davidson County, NC9.54
    3870746Davidson County, TN9.12
    26.6434072Davis County, UT7.41
    44.3270179DeKalb County, GA10.70
    60.717341DeKalb County, IL7.53
    56.5315346DeSoto County, MS9.96
    83.147493Delaware County, IN7.69
    29.7614891Delaware County, OH6.53
    47.7944118Delaware County, PA8.56
    31.7975980Denton County, TX7.44
    21.3164002Denver County, CO9.97
    21.3413013Deschutes County, OR6.50
    16.4159412District of Columbia, DC10.07
    70.0817975Dona Ana County, NM8.19
    50.0313688Dorchester County, SC9.18
    13.0425912Douglas County, CO8.76
    52.9511757Douglas County, GA10.92
    51.047191Douglas County, KS6.60
    55.9256047Douglas County, NE8.94
    53.806999Douglas County, OR6.39
    34.3068211DuPage County, IL6.87
    41.8828912Durham County, NC8.83
    38.3018277Dutchess County, NY7.42
    55.5489270Duval County, FL10.39
    61.8338895East Baton Rouge Parish, LA12.33
    63.597301Eaton County, MI7.86
    66.9920874Ector County, TX9.26
    17.7110781El Dorado County, CA6.05
    32.7363679El Paso County, CO9.65
    74.5078465El Paso County, TX9.30
    67.6520605Elkhart County, IN6.82
    45.5618052Ellis County, TX7.30
    62.2965100Erie County, NY8.98
    74.5718441Erie County, PA9.13
    62.7626111Escambia County, FL10.78
    21.9759384Essex County, MA7.26
    33.0369651Essex County, NJ9.26
    79.308297Etowah County, AL8.03
    14.2989085Fairfax County, VA7.05
    26.8569289Fairfield County, CT7.22
    53.0811758Fairfield County, OH7.21
    64.8910394Faulkner County, AR7.65
    31.836286Fayette County, GA9.46
    55.1126238Fayette County, KY9.23
    82.198340Fayette County, PA8.56
    77.0311123Florence County, SC13.09
    64.437111Fond du Lac County, WI6.31
    22.2416062Forsyth County, GA6.84
    62.4330894Forsyth County, NC10.40
    37.6364832Fort Bend County, TX8.77
    62.338030Franklin County, MO7.42
    55.13123800Franklin County, OH9.29
    58.8411941Franklin County, PA6.90
    27.9421568Frederick County, MD6.61
    46.3496600Fresno County, CA7.76
    36.0186524Fulton County, GA11.37
    50.2827382Galveston County, TX8.83
    62.5318847Gaston County, NC10.28
    73.7130357Genesee County, MI10.49
    4520365Gloucester County, NJ7.79
    61.4811943Grayson County, TX7.44
    68.7823058Greene County, MO8.16
    56.8611888Greene County, OH6.86
    52.1945163Greenville County, SC8.48
    71.5511625Gregg County, TX8.94
    49.2113972Guadalupe County, TX7.62
    62.3941153Guilford County, NC10.02
    41.2176833Gwinnett County, GA9.25
    49.0318786Hall County, GA6.80
    33.4326854Hamilton County, IN6.49
    59.8072644Hamilton County, OH9.90
    51.8030828Hamilton County, TN8.71
    54.4833272Hampden County, MA8.96
    37.366428Hampshire County, MA6.40
    60.2211058Hampton city, VA10.17
    64.329474Hardin County, KY7.58
    36.7118296Harford County, MD7.55
    63.6113138Harnett County, NC8.33
    55.59455394Harris County, TX9.17
    69.8517487Harrison County, MS10.87
    47.6062452Hartford County, CT8.64
    29.5314568Hawaii County, HI8.70
    40.6621150Hays County, TX6.97
    49.597168Henderson County, NC7.53
    45.8812504Hendricks County, IN6.43
    36.21103352Hennepin County, MN7.74
    42.8225990Henrico County, VA8.35
    49.7419461Henry County, GA12.03
    60.0411629Hernando County, FL8.33
    83.0496697Hidalgo County, TX9.29
    45.98119285Hillsborough County, FL9.03
    35.4829024Hillsborough County, NH6.91
    80.5119288Hinds County, MS15.39
    11.8778677Honolulu County, HI8.52
    57.8022858Horry County, SC8.36
    74.549155Houston County, AL10.05
    64.7413805Houston County, GA9.57
    19.3522481Howard County, MD8.32
    24.7965616Hudson County, NJ8.28
    36.228646Humboldt County, CA5.54
    22.687266Hunterdon County, NJ4.94
    57.4116878Imperial County, CA6.24
    49.198699Indian River County, FL7.33
    6820257Ingham County, MI8.71
    50.7513891Iredell County, NC8.29
    72.3811398Jackson County, MI9.02
    64.7460827Jackson County, MO9.83
    71.1310872Jackson County, MS9.68
    36.2414713Jackson County, OR6.98
    77.7110937Jasper County, MO7.44
    62.6056397Jefferson County, AL11.36
    19.1238651Jefferson County, CO9.02
    60.1867103Jefferson County, KY9.39
    59.6616932Jefferson County, MO8.20
    70.7512213Jefferson County, NY7.56
    75.1122535Jefferson County, TX10.73
    60.1737531Jefferson Parish, LA10.22
    48.2511748Johnson County, IA6.42
    52.4913231Johnson County, IN7.34
    35.2748504Johnson County, KS6.53
    55.5116420Johnson County, TX6.66
    53.6918770Johnston County, NC8.05
    60.9619313Kalamazoo County, MI7.94
    80.0911993Kanawha County, WV10.63
    45.7240039Kane County, IL7.43
    69.718127Kankakee County, IL8.33
    50.7816592Kaufman County, TX7.73
    42.2310514Kendall County, IL6.35
    64.607573Kennebec County, ME6.75
    54.9612018Kenosha County, WI7.20
    51.0314752Kent County, DE9.39
    51.7557233Kent County, MI8.79
    39.6510222Kent County, RI6.38
    58.6515280Kenton County, KY7.69
    52.6386859Kern County, CA7.65
    12.92163987King County, WA6.98
    51.6215013Kings County, CA6.52
    9.96243582Kings County, NY7.87
    24.3719887Kitsap County, WA6.59
    52.4937089Knox County, TN8.13
    30.0613287Kootenai County, ID5.04
    58.767890La Crosse County, WI5.81
    70.577995La Porte County, IN8.12
    73.647663LaSalle County, IL6.66
    70.8214150Lackawanna County, PA8.38
    60.4823128Lafayette Parish, LA9.70
    52.5525103Lake County, FL8.56
    42.1547218Lake County, IL7.64
    65.6737650Lake County, IN8.95
    62.5014729Lake County, OH7.18
    55.7326011Lancaster County, NE7.04
    49.5648591Lancaster County, PA6.29
    37.2121449Lane County, OR6.59
    24.1821477Larimer County, CO8.72
    60.5610966Lebanon County, PA7.23
    59.1513390Lee County, AL9.61
    47.6151118Lee County, FL8.64
    54.7528087Lehigh County, PA8.38
    57.9719801Leon County, FL11.05
    62.0222719Lexington County, SC8.84
    55.1213283Licking County, OH7.21
    63.3118307Linn County, IA6.80
    43.3210146Linn County, OR6
    43.139953Litchfield County, CT5.58
    40.2011994Livingston County, MI6.22
    61.0212929Livingston Parish, LA8.21
    64.5922154Lorain County, OH8.77
    14.23688901Los Angeles County, CA7.54
    11.9433757Loudoun County, VA6.65
    73.9611240Lowndes County, GA11.63
    67.2628358Lubbock County, TX8.81
    74.4334713Lucas County, OH9.97
    75.4822473Luzerne County, PA8.39
    69.887892Lycoming County, PA7.39
    58.7261638Macomb County, MI9.18
    81.618213Macon County, IL11.12
    43.7714714Madera County, CA6
    53.8030893Madison County, AL10.12
    68.9218745Madison County, IL8.81
    78.219983Madison County, IN8.79
    78.5416277Mahoning County, OH10.81
    46.7425916Manatee County, FL8.09
    64.3610200Marathon County, WI6.25
    36.11354643Maricopa County, AZ7.64
    4.8915052Marin County, CA5.01
    66.5925152Marion County, FL8.72
    67.0298934Marion County, IN10
    38.9927904Marion County, OR6.49
    40.778868Martin County, FL6.15
    11.5911878Maui County, HI7.34
    45.4821327McHenry County, IL6.44
    63.4211786McLean County, IL7.26
    66.2023344McLennan County, TX8.66
    40.70104482Mecklenburg County, NC9.65
    49.0611554Medina County, OH5.68
    42.3126538Merced County, CA6.40
    42.5028605Mercer County, NJ7.89
    77.087124Mercer County, PA7.78
    41.738984Merrimack County, NH5.77
    42.8010649Mesa County, CO8.12
    63.708098Miami County, OH5.29
    37.24204515Miami-Dade County, FL8.08
    39.089099Middlesex County, CT6.57
    14.53112506Middlesex County, MA7.06
    29.1859673Middlesex County, NJ8.11
    48.7021004Midland County, TX7.75
    66.7984871Milwaukee County, WI11.06
    52.5819552Minnehaha County, SD7.16
    33.027492Missoula County, MT7.06
    72.9536155Mobile County, AL12.23
    60.9012258Mohave County, AZ7.01
    20.2442807Monmouth County, NJ6.92
    53.667584Monroe County, IN7.39
    62.3910396Monroe County, MI7.02
    65.3052483Monroe County, NY9.38
    55.799662Monroe County, PA8.58
    16.9038951Monterey County, CA6.57
    74.3421006Montgomery County, AL13.32
    18.9381398Montgomery County, MD7.43
    72.9543206Montgomery County, OH9.19
    31.4159114Montgomery County, PA7.42
    56.8625284Montgomery County, TN8.84
    43.0356753Montgomery County, TX7.44
    71.6210187Morgan County, AL8.41
    19.3533488Morris County, NJ6.06
    24.4352583Multnomah County, OR7.18
    73.5518953Muscogee County, GA12.06
    73.2913260Muskegon County, MI9.79
    12.888402Napa County, CA5.36
    13.8196140Nassau County, NY8.10
    74.738909Navajo County, AZ7.77
    43.8242669New Castle County, DE9.35
    43.4515175New Hanover County, NC8.74
    48.1059132New Haven County, CT8.37
    46.9917374New London County, CT7.54
    8.92103804New York County, NY8.22
    62.7417861Newport News city, VA10.06
    7113750Niagara County, NY8.62
    14.9949215Norfolk County, MA6.83
    53.5122047Norfolk city, VA11.02
    50.0319439Northampton County, PA7.77
    68.2230358Nueces County, TX8.96
    43.6588000Oakland County, MI8.11
    35.1469158Ocean County, NJ5.77
    45.2118428Okaloosa County, FL8.23
    66.3277198Oklahoma County, OK9.12
    45.2413733Olmsted County, MN6.69
    72.8116435Oneida County, NY8.61
    67.4733511Onondaga County, NY8.65
    63.4626615Onslow County, NC7.05
    62.356746Ontario County, NY6.24
    11.18224357Orange County, CA6.80
    44.12114737Orange County, FL9.12
    31.238057Orange County, NC7.90
    36.7037934Orange County, NY6.93
    51.5529500Orleans Parish, LA12.43
    47.6633136Osceola County, FL8.54
    78.338126Oswego County, NY7.29
    47.3221833Ottawa County, MI6.22
    74.8113939Ouachita Parish, LA13.14
    55.4414935Outagamie County, WI6.17
    38.83103939Palm Beach County, FL8.85
    4012572Parker County, TX6.12
    55.4438238Pasco County, FL8.06
    34.5444279Passaic County, NJ9.01
    46.1412685Paulding County, GA8.90
    53.499998Pennington County, SD6.77
    68.968987Penobscot County, ME6.09
    74.6915375Peoria County, IL9.90
    62.40136032Philadelphia County, PA11.07
    65.168567Pickens County, SC7.57
    26.2376617Pierce County, WA6.99
    53.4070658Pima County, AZ8.29
    50.2334632Pinal County, AZ7.09
    48.0752352Pinellas County, FL8.31
    71.0714425Pitt County, NC11.62
    15.8726154Placer County, CA5.53
    23.1336711Plymouth County, MA7.07
    62.5960308Polk County, FL9.18
    55.0545272Polk County, IA7.60
    63.479502Portage County, OH7.17
    52.8211257Porter County, IN6.91
    81.0911015Potter County, TX9.43
    33.0578003Prince George's County, MD9.51
    23.3343996Prince William County, VA7.55
    42.9348401Providence County, RI8.25
    58.0412052Pueblo County, CO10.64
    68.1034780Pulaski County, AR11.78
    16.43175615Queens County, NY9.07
    59.8515175Racine County, WI8.77
    46.6047539Ramsey County, MN8.41
    58.1611721Randall County, TX7.58
    75.2910893Randolph County, NC8.40
    61.4512159Rankin County, MS10.38
    74.6411353Rapides Parish, LA11.97
    56.8710764Rensselaer County, NY7.52
    78.329503Richland County, OH6.94
    64.4432209Richland County, SC11.42
    76.9019804Richmond County, GA12.49
    15.9435393Richmond County, NY8.02
    49.7920920Richmond city, VA10.97
    28.37192414Riverside County, CA7.22
    93.1212742Robeson County, NC11.58
    64.4712737Rock County, WI8.23
    76.8111018Rock Island County, IL8.57
    25.7619034Rockingham County, NH6.17
    21.1043343Rockland County, NY5.69
    66.2011123Rowan County, NC9.62
    41.4830611Rutherford County, TN8.60
    27.87127643Sacramento County, CA7.21
    78.7413891Saginaw County, MI9.77
    62.299615Saline County, AR7.85
    27.27105826Salt Lake County, UT7.73
    31.95187306San Bernardino County, CA8.13
    13.98262290San Diego County, CA6.94
    3.1553480San Francisco County, CA7.21
    28.6468585San Joaquin County, CA7.71
    75.949185San Juan County, NM7.20
    12.6916917San Luis Obispo County, CA5.98
    3.1853632San Mateo County, CA6.67
    50.909297Sandoval County, NM8.48
    69.7614439Sangamon County, IL11.58
    17.0238130Santa Barbara County, CA6.56
    5.05137356Santa Clara County, CA7.29
    8.5815846Santa Cruz County, CA5.74
    38.817907Santa Fe County, NM10.29
    48.3013795Santa Rosa County, FL7.79
    38.8720475Sarasota County, FL7.49
    40.8714113Saratoga County, NY6.19
    45.8216792Sarpy County, NE7.14
    62.4612448Schenectady County, NY9.05
    79.378894Schuylkill County, PA7.65
    61.4113720Scott County, IA7.73
    31.0711747Scott County, MN6.25
    77.3611210Sebastian County, AR8.01
    68.5346179Sedgwick County, KS8.35
    40.3831709Seminole County, FL7.92
    44.0512870Shasta County, CA6.40
    72.5813889Shawnee County, KS8.03
    62.288041Sheboygan County, WI6.60
    45.8716085Shelby County, AL8.56
    66.3086868Shelby County, TN11.97
    28.349624Skagit County, WA5.18
    63.0821093Smith County, TX7.76
    17.5568121Snohomish County, WA6.71
    20.5634136Solano County, CA7.36
    21.6322160Somerset County, NJ7.02
    14.2530993Sonoma County, CA5.89
    66.4828675Spartanburg County, SC8.78
    40.6440755Spokane County, WA6.89
    33.9511116Spotsylvania County, VA7.35
    44.1529232St. Charles County, MO7.29
    70.5719164St. Clair County, IL11.12
    64.3910308St. Clair County, MI6.64
    29.1016651St. Johns County, FL6.88
    71.7122927St. Joseph County, IN8.93
    83.176920St. Lawrence County, NY6.09
    63.2912515St. Louis County, MN6.79
    53.5773959St. Louis County, MO10.13
    70.8425311St. Louis city, MO12.45
    50.8023974St. Lucie County, FL9.01
    31.679557St. Mary's County, MD6.37
    50.7520203St. Tammany Parish, LA8.56
    24.6312630Stafford County, VA7.75
    33.7749716Stanislaus County, CA6.54
    71.6127695Stark County, OH8.52
    54.0314064Stearns County, MN6.36
    40.558060Strafford County, NH6.23
    16.5459170Suffolk County, MA8.20
    19.74108298Suffolk County, NY8.06

    The first 500 of 578 rows; every row is in figures/lbw_by_deprivation.json.

    Table 2.2. Preterm and low birthweight

    Preterm birth is more common than low birthweight in every decile and rises more, from 8.8% to 12.1%

    Births-weighted share of live births before 37 weeks and under 2,500 grams by decile of county deprivation, 2018 to 2024

    conf_highconf_lowdecileestimatemeasuren
    9.018.5918.82Preterm birth4,151,203
    7.687.1817.43Low birthweight4,150,007
    9.489.0829.28Preterm birth2,647,866
    8.007.3227.63Low birthweight2,646,210
    10.129.4739.82Preterm birth2,523,259
    8.367.5537.96Low birthweight2,522,181
    10.299.80410.05Preterm birth1,825,582
    8.677.8448.29Low birthweight1,824,679
    10.539.98510.27Preterm birth1,923,159
    8.657.9758.37Low birthweight1,922,260
    11.2810.26610.80Preterm birth2,196,492
    8.988.2968.69Low birthweight2,195,346
    11.2210.56710.92Preterm birth1,520,420
    9.508.5779.05Low birthweight1,519,471
    11.5910.92811.27Preterm birth1,469,109
    9.858.8989.40Low birthweight1,468,025
    11.8211.01911.42Preterm birth1,269,566
    10.189.0099.63Low birthweight1,268,228
    12.6611.321012.05Preterm birth891,594
    10.269.20109.68Low birthweight890,018

    Table 2.3. All counties

    Across all counties with a published rate the share is 7.6% in the least deprived tenth and 10.9% in the most deprived, and levels off in between

    Births-weighted low-birthweight share by decile of county deprivation rank, 3,040 counties, County Health Rankings, births in 2016 to 2022

    conf_highconf_lowdecileestimaten
    7.777.4117.5810,018,514
    8.448.0028.244,922,587
    8.818.3638.623,381,491
    9.508.7449.142,597,848
    9.658.7059.191,741,523
    9.568.8069.171,216,083
    9.298.5678.89846,209
    9.438.9589.17752,806
    10.239.5399.88447,237
    11.3010.561010.93327,359

    Note: The counties are the 578 that WONDER natality names individually (at least 100,000 residents), which hold 79.5% of births. WONDER pools the births of every other county in each state, so those counties are not in this figure.

    Note: A county's deprivation rank is the population-weighted mean of the Area Deprivation Index national ranks of its census tracts (1 is least deprived, 100 most), weighted by 2019-2023 tract population. Deciles hold equal numbers of these counties, so the most deprived tenth is relative to large counties and not to the nation.

    Note: WONDER withholds cells of 1 to 9 births. A withheld cell is missing: it is left out of both the count and the denominator. The birthweight cut has 11,250 withheld cells in these counties; at 9 births each they could hold at most 0.5% of births, so a pooled share could move by at most that many percentage points.

    Note: Decile means are births-weighted. Intervals are 95% intervals from a bootstrap over counties, described in the methods note. The rates pool births in 2018 to 2024.

    Note: The third tab uses County Health Rankings rates for every county with a published rate, not the WONDER counts, and deciles of all counties, so its most deprived tenth is made up of small counties.

    Source: CDC WONDER natality, births in 2018-2024, and Area Deprivation Index 2023; full counts of births, county shares weighted by births (population-weighted); third tab: County Health Rankings 2024, births in 2016-2022, births-weighted (population-weighted)

    Data: vishalsingh.org/zipcode/report/birthweight-and-preterm-birth/figures/lbw_by_deprivation.json

    Table 3. Non-Hispanic Black mothers had low-birthweight births at 14.0% against 6.7% for non-Hispanic white mothers, a ratio of 2.1

    First panel: share of live births under 2,500 grams in the large counties, by mother's race and ethnicity, County Health Rankings, births in 2016 to 2022. Second panel: infant deaths per 1,000 live births in the United States by mother's single race, any ethnicity, 2018 and 2019

    conf_highconf_lowlabelnpanelracevalue
    14.1913.75Black (non-Hispanic)3,249,387Low birthweight (% of live births)Black13.98
    7.707.39Hispanic (any race)5,632,060Low birthweight (% of live births)Hispanic7.54
    6.826.64White (non-Hispanic)9,614,256Low birthweight (% of live births)White6.73
    10.4910.14Black (any ethnicity)1,255,629Infant mortality (deaths per 1,000 live births)Black10.32
    4.784.66White (any ethnicity)5,617,093Infant mortality (deaths per 1,000 live births)White4.72

    Note: Low birthweight comes from County Health Rankings county rates for the 578 large counties. County Health Rankings counts mothers as non-Hispanic Black, non-Hispanic white or Hispanic of any race. It publishes each rate with its interval but not the births behind it; the births are recovered from the interval, and each group's rate is pooled over the counties where the rate is published.

    Note: Infant mortality is pooled over states, so it covers all counties, not only the large ones. WONDER's linked file counts mothers by single race of any ethnicity, so its white group includes Hispanic mothers and is not the same group as in the first panel. WONDER withholds a state's deaths for a race with 1 to 9 deaths; those cells leave both the deaths and the births.

    Note: Low-birthweight intervals come from a bootstrap that resamples whole counties. Infant mortality intervals are gamma or normal intervals on the count, which treat births as independent and leave out differences between states.

    Source: County Health Rankings 2024, births in 2016-2022 (rates pooled by births, population-weighted); CDC WONDER linked birth and infant death, 2018-2019, mother's race (crude rates)

    Data: vishalsingh.org/zipcode/report/birthweight-and-preterm-birth/figures/birth_outcomes_by_race.json

    Table 4. Low birthweight is more common for non-Hispanic Black mothers in the least deprived quartile of counties (12.4%) than for non-Hispanic white mothers in the most deprived (7.6%)

    Low birthweight (share of live births under 2,500 grams, births in 2016 to 2022) or infant mortality (deaths per 1,000 live births, 2018 and 2019) by quartile of county deprivation rank and mother's race

    conf_highconf_lowcountiesmeasurenquartileracerate
    12.7611.95133lbw830,778Least deprived quartileBlack (non-Hispanic)12.37
    6.346.05144lbw3,597,717Least deprived quartileWhite (non-Hispanic)6.18
    14.0213.46137lbw862,783Second quartileBlack (non-Hispanic)13.76
    6.756.53145lbw2,307,987Second quartileWhite (non-Hispanic)6.64
    14.7814.14139lbw823,241Third quartileBlack (non-Hispanic)14.46
    7.237.05144lbw2,156,968Third quartileWhite (non-Hispanic)7.14
    15.8015.25140lbw732,585Most deprived quartileBlack (non-Hispanic)15.53
    7.707.45145lbw1,551,584Most deprived quartileWhite (non-Hispanic)7.58
    9.297.8765imr229,878Least deprived quartileBlack (any ethnicity)8.55
    43.5495imr1,555,633Least deprived quartileWhite (any ethnicity)3.76
    10.739.5143imr214,646Second quartileBlack (any ethnicity)10.15
    4.744.1958imr728,879Second quartileWhite (any ethnicity)4.47
    12.0710.6839imr200,671Third quartileBlack (any ethnicity)11.33
    5.424.8750imr602,598Third quartileWhite (any ethnicity)5.12
    13.2411.5433imr148,514Most deprived quartileBlack (any ethnicity)12.45
    5.674.9339imr338,122Most deprived quartileWhite (any ethnicity)5.29

    Views: Low birthweight (measure = lbw); Infant mortality (measure = imr).

    Note: Counties are the 578 large counties, ranked by deprivation as in the gradient figure. The low-birthweight view pools County Health Rankings rates over the counties where each group's rate is published, for non-Hispanic Black and non-Hispanic white mothers; the counts of counties are in the data table.

    Note: The infant mortality view covers counties of 250,000 residents or more, where WONDER lists deaths by mother's race, for births in 2018 and 2019, with mothers counted by single race of any ethnicity (the white group includes Hispanic mothers). WONDER withholds a county-year with 1 to 9 deaths. Those county-years are left out of both deaths and births, which removes 13.6% of Black births and 5.2% of white births in these counties, so the bars describe the county-years with at least 10 infant deaths.

    Note: Intervals are 95% intervals from a bootstrap that resamples whole counties, described in the methods note, with the same draws for both groups so that gaps have their own interval.

    Source: County Health Rankings 2024, births in 2016-2022, and CDC WONDER linked birth and infant death, 2018-2019; rates pooled by births (population-weighted)

    Data: vishalsingh.org/zipcode/report/birthweight-and-preterm-birth/figures/weathering.json

    Table 5. Low birthweight is steadily worse toward the more deprived end under the ADI; the two ends do not differ detectably under the degree-share ranking

    Births under 2,500 grams (% of live births) by tenth of counties ranked four ways, over the 578 counties that have all four rankings

    binconf_highconf_lowestimaten_unitsranking
    17.687.187.4357Area Deprivation Index
    28.007.327.6358Area Deprivation Index
    38.477.638.0758Area Deprivation Index
    48.527.748.1558Area Deprivation Index
    58.637.998.3658Area Deprivation Index
    69.018.298.7357Area Deprivation Index
    79.508.599.0458Area Deprivation Index
    89.588.689.1558Area Deprivation Index
    910.369.289.8658Area Deprivation Index
    1010.179.149.6358Area Deprivation Index
    17.326.967.1657Standardized index
    27.467.037.2458Standardized index
    38.427.417.9258Standardized index
    48.627.918.2458Standardized index
    58.547.758.1758Standardized index
    68.857.898.2857Standardized index
    79.158.548.8658Standardized index
    89.228.648.9358Standardized index
    910.158.789.4258Standardized index
    1010.378.989.7358Standardized index
    17.326.997.1657Median household income
    27.647.047.3358Median household income
    38.437.658.0158Median household income
    48.447.718.0158Median household income
    58.708.038.4058Median household income
    68.958.328.7257Median household income
    78.878.268.5658Median household income
    89.468.549.0358Median household income
    910.499.5510.0858Median household income
    1010.659.429.9958Median household income
    17.957.227.5557Bachelor's degree share
    28.437.668.0458Bachelor's degree share
    38.417.567.9558Bachelor's degree share
    48.607.798.2658Bachelor's degree share
    58.938.018.4658Bachelor's degree share
    69.157.998.4357Bachelor's degree share
    79.428.488.9658Bachelor's degree share
    89.398.569.0158Bachelor's degree share
    99.668.128.8558Bachelor's degree share
    108.587.768.1658Bachelor's degree share

    Note: Least and most deprived tenth: ADI 7.4% and 9.6%, rank correlation +0.99; standardized index 7.2% and 9.7%, +0.99; median household income 7.2% and 10.0%, +0.96; bachelor's degree share 7.6% and 8.2%, +0.68.

    Note: The standardized index applies the ADI's coefficients to its measures after standardizing each one, so home value and income carry less weight than in the ADI. Income and degree share are single census measures, each ranked from the highest value to the lowest.

    Source: CDC WONDER natality, births in 2018-2024, and Area Deprivation Index 2023; full counts of births, county shares weighted by births (population-weighted); ADI 2023 and ACS 2019-2023 tract tables (B19013, B15003 and the 15 rebuilt ADI measures)

    Data: vishalsingh.org/zipcode/report/birthweight-and-preterm-birth/figures/alt_rankings.json

    All estimates

    Every fact in facts.json (79), sorted by id. The same values as JSON: facts.json.

    Fact idValueUnitEstimandPopulationPeriodIntervalnWeightsSourceNote
    alt_adi_least7.4%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe least deprived tenth of counties ranked by Area Deprivation Index, among the counties with all four rankingsbirths in 2018 to 202495% CI 7.2% to 7.7%57 countiesbirths in each countyCDC WONDER natality
    alt_adi_most9.6%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe most deprived tenth of counties ranked by Area Deprivation Index, among the counties with all four rankingsbirths in 2018 to 202495% CI 9.1% to 10.2%58 countiesbirths in each countyCDC WONDER natality
    alt_adi_rho+0.99rank correlationSpearman rank correlation between bin order and bin mean, each bin counted oncethe bins of counties ranked by Area Deprivation Indexbirths in 2018 to 2024each bin counted onceCDC WONDER natality
    alt_degree_least7.6%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe least deprived tenth of counties ranked by Bachelor's degree share, among the counties with all four rankingsbirths in 2018 to 202495% CI 7.2% to 7.9%57 countiesbirths in each countyCDC WONDER natality
    alt_degree_most8.2%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe most deprived tenth of counties ranked by Bachelor's degree share, among the counties with all four rankingsbirths in 2018 to 202495% CI 7.8% to 8.6%58 countiesbirths in each countyCDC WONDER natality
    alt_degree_rho+0.68rank correlationSpearman rank correlation between bin order and bin mean, each bin counted oncethe bins of counties ranked by Bachelor's degree sharebirths in 2018 to 2024each bin counted onceCDC WONDER natality
    alt_income_least7.2%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe least deprived tenth of counties ranked by Median household income, among the counties with all four rankingsbirths in 2018 to 202495% CI 7.0% to 7.3%57 countiesbirths in each countyCDC WONDER natality
    alt_income_most10.0%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe most deprived tenth of counties ranked by Median household income, among the counties with all four rankingsbirths in 2018 to 202495% CI 9.4% to 10.6%58 countiesbirths in each countyCDC WONDER natality
    alt_income_rho+0.96rank correlationSpearman rank correlation between bin order and bin mean, each bin counted oncethe bins of counties ranked by Median household incomebirths in 2018 to 2024each bin counted onceCDC WONDER natality
    alt_n_places578countiescount of counties in the common sample of the ranking comparisoncounties with the outcome and all four rankingsbirths in 2018 to 2024none (full count)CDC WONDER natality
    alt_rho_cut0.9absolute rank correlationthreshold between a steady and an uneven gradientthe rule for changed gradients (docs/RANKING_SWITCH_RULE.md)births in 2018 to 2024none (a fixed rule)CDC WONDER natality
    alt_rho_margin0.1absolute rank correlationsmallest move in the rank correlation that counts as a change of shapethe rule for changed gradients (docs/RANKING_SWITCH_RULE.md)births in 2018 to 2024none (a fixed rule)CDC WONDER natality
    alt_std_least7.2%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe least deprived tenth of counties ranked by Standardized index, among the counties with all four rankingsbirths in 2018 to 202495% CI 7.0% to 7.3%57 countiesbirths in each countyCDC WONDER natality
    alt_std_most9.7%Births under 2,500 grams (% of live births)births-weighted mean of county shares (the pooled share); 95% intervals from a bootstrap over countiesthe most deprived tenth of counties ranked by Standardized index, among the counties with all four rankingsbirths in 2018 to 202495% CI 9.0% to 10.4%58 countiesbirths in each countyCDC WONDER natality
    alt_std_rho+0.99rank correlationSpearman rank correlation between bin order and bin mean, each bin counted oncethe bins of counties ranked by Standardized indexbirths in 2018 to 2024each bin counted onceCDC WONDER natality
    births_20183.79 millionlive birthscount of live birthslive births in the United States2018none (full count)CDC WONDER natality
    births_20243.63 millionlive birthscount of live birthslive births in the United States2024none (full count)CDC WONDER natality
    births_covered20.5 millionlive birthscount of live birthslive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more)births in 2018 to 202420,450,654 birthsnone (full count)CDC WONDER natality
    births_decline_pct4.3%percent of 2018 birthsfall in the count of births from 2018 to 2024live births in the United States2018 to 2024none (full count)CDC WONDER natality
    births_median_all_d112,055live birthsmedian of the county birth counts behind the rate (CHR denominator)the median county in the least deprived tenth of all counties with a County Health Rankings rate and an ADIbirths in 2016 to 2022304 countiesnone (each county counts once)County Health Rankings
    births_median_all_d10770live birthsmedian of the county birth counts behind the rate (CHR denominator)the median county in the most deprived tenth of all counties with a County Health Rankings rate and an ADIbirths in 2016 to 2022304 countiesnone (each county counts once)County Health Rankings
    births_share_covered79.5%percent of live births in the United Statesshare of births in the named countieslive births in the 50 states and DCbirths in 2018 to 202425,709,900 birthsnone (full count)CDC WONDER natality
    chr_wonder_corr0.984correlation coefficientbirths-weighted correlation between the county low-birthweight share in WONDER and in County Health Rankings, county-cluster bootstrap intervalthe named countiesWONDER births in 2018 to 2024 and CHR births in 2016 to 202295% CI 0.980 to 0.987578 countiesWONDER births in each countyCounty Health Rankings
    counties_all_gradient3,040countiescount of countiescounties with a County Health Rankings low-birthweight rate and an ADIbirths in 2016 to 2022none (full count)County Health Rankings
    counties_below_floor145countiescount of counties with a rate but fewer than 20 low-birthweight births, which the map leaves as no datacounties and county equivalents on the map (50 states and DC)births in 2016 to 2022none (full count)County Health Rankings
    counties_mapped2,900countiescount of counties with a rate and at least 20 low-birthweight birthscounties and county equivalents on the map (50 states and DC)births in 2016 to 2022none (full count)County Health Rankings
    counties_no_rate98countiescount of counties for which County Health Rankings publishes no low-birthweight ratecounties and county equivalents on the map (50 states and DC)births in 2016 to 2022none (full count)County Health Rankings
    counties_not_mapped243countiescount of counties with no rate or fewer than 20 low-birthweight birthscounties and county equivalents on the map (50 states and DC)births in 2016 to 2022none (full count)County Health Rankings
    counties_used578countiescount of countiescounties that WONDER natality names individually and that have birthsbirths in 2018 to 2024none (full count)CDC WONDER natality
    deep_south_all_share14%percent of countiesshare of mapped counties in Alabama, Georgia, Louisiana, Mississippi and South Carolinaall mapped countiesbirths in 2016 to 20222,900 countiesnone (each county counts once)County Health Rankings
    deep_south_top_share64%percent of countiesshare of those counties in Alabama, Georgia, Louisiana, Mississippi and South Carolinamapped counties in the highest tenth of low-birthweight sharesbirths in 2016 to 2022290 countiesnone (each county counts once)County Health Rankings
    im_black10.3 deaths per 1,000 live birthsinfant deaths per 1,000 live birthscrude rate from state counts, normal intervallive births to Black mothers (single race, any ethnicity) in the United States, states with a published countbirths in 2018 and 201995% CI 10.10 to 10.5012,953 infant deathsnone (crude rate from counts)CDC WONDER linked birth and infant death
    im_left_out_black13.6%percent of live birthsshare of births in county-years whose deaths WONDER withholds, which the county view leaves out of deaths and birthslive births to black mothers (single race, any ethnicity) in counties of 250,000 residents or morebirths in 2018 and 2019none (full counts of births)CDC WONDER linked birth and infant death
    im_left_out_white5.2%percent of live birthsshare of births in county-years whose deaths WONDER withholds, which the county view leaves out of deaths and birthslive births to white mothers (single race, any ethnicity) in counties of 250,000 residents or morebirths in 2018 and 2019none (full counts of births)CDC WONDER linked birth and infant death
    im_white4.7infant deaths per 1,000 live birthscrude rate from state counts, normal intervallive births to white mothers (single race, any ethnicity) in the United States, states with a published countbirths in 2018 and 201995% CI 4.7 to 4.826,516 infant deathsnone (crude rate from counts)CDC WONDER linked birth and infant death
    lbd_county_threshold250,000residentspopulation size at which WONDER names a county in the linked file (a definition)counties that CDC WONDER linked birth and infant death names individuallybirths in 2018 and 2019none (definition)CDC WONDER linked birth and infant death
    lbw_adi_corr0.52correlation coefficientbirths-weighted correlation of the county low-birthweight share with county deprivation rank, county-cluster bootstrap intervallive births in the named countiesbirths in 2018 to 202495% CI 0.45 to 0.58578 countiesbirths in each countyCDC WONDER natality
    lbw_all_d17.6%percent of live births under 2,500 gramsbirths-weighted mean of county shares, bootstrap interval over countieslive births in the least deprived tenth of all counties with a County Health Rankings rate and an ADIbirths in 2016 to 202295% CI 7.4% to 7.8%304 countiesbirths in each county (CHR denominator)County Health Rankings
    lbw_all_d1010.9%percent of live births under 2,500 gramsbirths-weighted mean of county shares, bootstrap interval over countieslive births in the most deprived tenth of all counties with a County Health Rankings rate and an ADIbirths in 2016 to 202295% CI 10.6% to 11.3%304 countiesbirths in each county (CHR denominator)County Health Rankings
    lbw_b1_w4_diff4.8 percentage pointspercentage pointsdifference of two pooled low-birthweight shares, county-cluster bootstrap intervallive births in the named counties: non-Hispanic Black mothers in the least deprived quartile minus non-Hispanic white mothers in the most deprived quartilebirths in 2016 to 202295% CI 4.4 percentage points to 5.2 percentage points578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_black14.0%percent of live births under 2,500 gramspooled share of births, from the published county rates and the births they imply, bootstrap interval over countieslive births to non-Hispanic Black mothers in the named counties where County Health Rankings publishes the ratebirths in 2016 to 202295% CI 13.8% to 14.2%549 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_black_q112.4%percent of live births under 2,500 gramspooled share of births, bootstrap interval over countieslive births to non-Hispanic Black mothers in the least deprived quartile of the named counties by deprivation rankbirths in 2016 to 202295% CI 11.9% to 12.8%133 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_cutoff_grams2,500gramsbirthweight below which a live birth counts as low birthweight (a definition)live birthsall years (a definition)none (definition)CDC WONDER natality
    lbw_d17.4%percent of live births under 2,500 gramsbirths-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the least deprived tenth of the named counties by county deprivation rankbirths in 2018 to 202495% CI 7.2% to 7.7%57 countiesbirths in each countyCDC WONDER natality
    lbw_d109.7%percent of live births under 2,500 gramsbirths-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the most deprived tenth of the named counties by county deprivation rankbirths in 2018 to 202495% CI 9.2% to 10.3%58 countiesbirths in each countyCDC WONDER natality
    lbw_gap_pp7.3 percentage pointspercentage pointsdifference of pooled low-birthweight shares, county-cluster bootstrap intervallive births in the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersbirths in 2016 to 202295% CI 7.0 percentage points to 7.4 percentage points578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_gap_q16.2 percentage pointspercentage pointsdifference of pooled low-birthweight shares, county-cluster bootstrap intervallive births in the least deprived quartile of the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersbirths in 2016 to 202295% CI 5.8 percentage points to 6.6 percentage points578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_gap_q48.0 percentage pointspercentage pointsdifference of pooled low-birthweight shares, county-cluster bootstrap intervallive births in the most deprived quartile of the named counties, non-Hispanic Black mothers minus non-Hispanic white mothersbirths in 2016 to 202295% CI 7.7 percentage points to 8.2 percentage points578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_gap_widening1.8 percentage pointspercentage pointsdifference of two Black-white gaps in pooled low-birthweight shares, county-cluster bootstrap intervallive births in the named counties, gap between non-Hispanic Black and non-Hispanic white mothers in the most deprived quartile minus the gap in the least deprived quartilebirths in 2016 to 202295% CI 1.3 percentage points to 2.3 percentage points578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_hispanic7.5%percent of live births under 2,500 gramspooled share of births, from the published county rates and the births they imply, bootstrap interval over countieslive births to Hispanic (any race) mothers in the named counties where County Health Rankings publishes the ratebirths in 2016 to 202295% CI 7.4% to 7.7%575 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_natl8.3%percent of live births under 2,500 gramspooled share of births in published cells (events over births), Wilson intervallive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more), births in published cellsbirths in 2018 to 202495% CI 8.3% to 8.3%20,406,425 birthsnone (full counts of births)CDC WONDER natalityWONDER withholds cells of 1 to 9 births; a withheld cell is left out of both the count and the denominator.
    lbw_preterm_corr0.84correlation coefficientbirths-weighted correlation between the county low-birthweight share and the county preterm share, county-cluster bootstrap intervallive births in the named countiesbirths in 2018 to 202495% CI 0.81 to 0.87578 countiesbirths in each countyCDC WONDER natality
    lbw_range_pp2.3 percentage pointspercentage pointsdifference of two births-weighted decile means of the low-birthweight share, bootstrap interval over countieslive births in the named counties, most deprived tenth minus least deprived tenthbirths in 2018 to 202495% CI 1.7 percentage points to 2.9 percentage points578 countiesbirths in each countyCDC WONDER natality
    lbw_ratio_bw2.1ratio of ratesratio of pooled low-birthweight shares, county-cluster bootstrap intervallive births in the named counties, non-Hispanic Black mothers over non-Hispanic white mothersbirths in 2016 to 202295% CI 2.0 to 2.1578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_rest7.8%percent of live births under 2,500 gramspooled share of births, bootstrap interval over countieslive births in mapped counties outside the Census South regionbirths in 2016 to 202295% CI 7.7% to 8.0%1,529 countiesbirths in each county (CHR denominator)County Health Rankings
    lbw_slope_per_100.38 percentage pointspercentage points of the low-birthweight share per ten points of county deprivation rankbirths-weighted slope of the county low-birthweight share on county deprivation rank, county-cluster bootstrap intervallive births in the named countiesbirths in 2018 to 202495% CI 0.32 percentage points to 0.44 percentage points578 countiesbirths in each countyCDC WONDER natality
    lbw_south9.1%percent of live births under 2,500 gramspooled share of births, bootstrap interval over countieslive births in mapped counties in the Census South region (16 states and DC)births in 2016 to 202295% CI 9.0% to 9.3%1,371 countiesbirths in each county (CHR denominator)County Health Rankings
    lbw_wh_low_d11.0withheld cells per county-yearwithheld birthweight cells below the low-birthweight cutoff, per county-yearcounty-years of the least deprived tenth of the named countiesbirths in 2018 to 2024399 county-yearsnone (full count)CDC WONDER natality
    lbw_wh_low_d101.6withheld cells per county-yearwithheld birthweight cells below the low-birthweight cutoff, per county-yearcounty-years of the most deprived tenth of the named countiesbirths in 2018 to 2024406 county-yearsnone (full count)CDC WONDER natality
    lbw_wh_max_d10.2%percent of live birthslargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in these countieslive births in the least deprived tenth of the named countiesbirths in 2018 to 2024none (an upper limit from the cell count)CDC WONDER natality
    lbw_wh_max_d101.3%percent of live birthslargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in these countieslive births in the most deprived tenth of the named countiesbirths in 2018 to 2024none (an upper limit from the cell count)CDC WONDER natality
    lbw_white6.7%percent of live births under 2,500 gramspooled share of births, from the published county rates and the births they imply, bootstrap interval over countieslive births to non-Hispanic white mothers in the named counties where County Health Rankings publishes the ratebirths in 2016 to 202295% CI 6.6% to 6.8%578 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_white_q47.6%percent of live births under 2,500 gramspooled share of births, bootstrap interval over countieslive births to non-Hispanic white mothers in the most deprived quartile of the named counties by deprivation rankbirths in 2016 to 202295% CI 7.5% to 7.7%145 countiesbirths to mothers of the group in each countyCounty Health Rankings
    lbw_withheld_cells11,250withheld cellscount of cells with 1 to 9 births, which WONDER withholdscounty-year cells of the WONDER birthweight cut in the named countiesbirths in 2018 to 2024none (full count)CDC WONDER natality
    lbw_withheld_max_share0.5%percent of live birthslargest share of births the withheld birthweight cells could hold: 9 births in each withheld cell, over all births in the countieslive births in the named countiesbirths in 2018 to 2024none (an upper limit from the cell count)CDC WONDER natality
    map_floor_births20low-birthweight birthsfewest low-birthweight births for which a county is drawn (a floor set for this book)counties on the mapbirths in 2016 to 2022none (definition)County Health Rankings
    preterm_adi_corr0.69correlation coefficientbirths-weighted correlation of the county preterm share with county deprivation rank, county-cluster bootstrap intervallive births in the named countiesbirths in 2018 to 202495% CI 0.64 to 0.73578 countiesbirths in each countyCDC WONDER natality
    preterm_cutoff_weeks37completed weeks of gestationgestational age below which a live birth counts as preterm, obstetric estimate (a definition)live birthsall years (a definition)none (definition)CDC WONDER natality
    preterm_hi12.1%percent of live births before 37 weeksbirths-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the most deprived tenth of the named counties by county deprivation rankbirths in 2018 to 202495% CI 11.3% to 12.7%58 countiesbirths in each countyCDC WONDER natality
    preterm_lo8.8%percent of live births before 37 weeksbirths-weighted mean of county shares (the pooled share), bootstrap interval over countieslive births in the least deprived tenth of the named counties by county deprivation rankbirths in 2018 to 202495% CI 8.6% to 9.0%57 countiesbirths in each countyCDC WONDER natality
    preterm_natl10.1%percent of live births before 37 weekspooled share of births in published cells (events over births), Wilson intervallive births in the counties that CDC WONDER natality names individually (counties of 100,000 residents or more), births in published cellsbirths in 2018 to 202495% CI 10.1% to 10.1%20,418,250 birthsnone (full counts of births)CDC WONDER natality
    preterm_range_pp3.2 percentage pointspercentage pointsdifference of two births-weighted decile means of the preterm share, bootstrap interval over countieslive births in the named counties, most deprived tenth minus least deprived tenthbirths in 2018 to 202495% CI 2.5 percentage points to 3.9 percentage points578 countiesbirths in each countyCDC WONDER natality
    preterm_slope_per_100.49 percentage pointspercentage points of the preterm share per ten points of county deprivation rankbirths-weighted slope of the county preterm share on county deprivation rank, county-cluster bootstrap intervallive births in the named countiesbirths in 2018 to 202495% CI 0.44 percentage points to 0.55 percentage points578 countiesbirths in each countyCDC WONDER natality
    preterm_withheld_cells8,704withheld cellscount of cells with 1 to 9 births, which WONDER withholdscounty-year cells of the WONDER gestational-age cut in the named countiesbirths in 2018 to 2024none (full count)CDC WONDER natality
    preterm_withheld_max_share0.4%percent of live birthslargest share of births the withheld gestational-age cells could hold: 9 births in each withheld cell, over all births in the countieslive births in the named countiesbirths in 2018 to 2024none (an upper limit from the cell count)CDC WONDER natality
    south_all_share47%percent of countiesshare of mapped counties in the Census South region (16 states and DC)all mapped countiesbirths in 2016 to 20222,900 countiesnone (each county counts once)County Health Rankings
    south_top_share89%percent of countiesshare of those counties in the Census South region (16 states and DC)mapped counties in the highest tenth of low-birthweight sharesbirths in 2016 to 2022290 countiesnone (each county counts once)County Health Rankings
    wonder_suppression_floor10birthsa cell with fewer births than this is withheld (a definition)cells of the WONDER natality filesbirths in 2018 to 2024none (definition)CDC WONDER natality
    wonder_threshold100,000residentspopulation size at which WONDER names a county (a definition)counties that CDC WONDER natality names individuallybirths in 2018 to 2024none (definition)CDC WONDER natality

    Definitions

    Low birthweight
    A live birth weighing less than 2,500 grams, the cutoff used in vital statistics.
    Preterm birth
    A birth before 37 weeks of pregnancy.
    Area Deprivation Index (ADI)
    A score that ranks neighborhoods by income, education, employment and housing conditions drawn from the American Community Survey. In this book a higher national percentile means a more deprived neighborhood.
    Suppression
    The withholding of a number because the count behind it is too small to publish without risking the identification of a person. A suppressed value is missing, not zero.
    Weathering
    The hypothesis that chronic stress from disadvantage and discrimination wears down health faster, so that the same outcomes appear at younger ages in affected groups. Arline Geronimus proposed it in studies of birth outcomes.
    EITC
    The Earned Income Tax Credit, a refundable federal tax credit for low and moderate income workers. It grows with earnings up to a limit and then phases out.

    Methods

    The county deprivation comparison uses births in 2018 to 2024 in the 578 counties that CDC WONDER names individually, the counties of 100,000 residents or more, which hold 79.5% of births. Smaller counties are not part of the WONDER figures. The comparisons by mother's race use other sources and birth periods: County Health Rankings rates for births in 2016 to 2022, and WONDER linked birth and infant death records for 2018 and 2019. Coverage and denominators differ across these sources, so each is described separately below.

    The county comparison uses only counties that WONDER names

    Low birthweight is a live birth under 2,500 grams and preterm birth one before 37 completed weeks (obstetric estimate).

    Counts come from CDC WONDER natality for 2018 to 2024, for the 578 counties that WONDER names individually (counties of 100,000 residents or more, 79.5% of births); WONDER pools every other county in a state into one Unidentified Counties row, which is not used. WONDER's 2024 natality data are final.

    Figure explained here: Figure 2

    Rates by mother's race and the map use other sources and birth periods

    Race-specific low birthweight comes from County Health Rankings county rates for births in 2016 to 2022, for non-Hispanic Black, non-Hispanic white and Hispanic (any race) mothers: CHR publishes each rate with a 95% interval, from which the births behind the rate are recovered, and the rates are pooled by births over the counties where a rate is published.

    Infant mortality by mother's race comes from WONDER linked birth and infant death for 2018 and 2019, the only years with mother's race, with mothers counted by single race of any ethnicity: national rates pool the state files, and the county view covers counties of 250,000 residents or more, with county-years that have withheld deaths left out of both deaths and births.

    The map shows County Health Rankings rates for every county with at least 20 low-birthweight births.

    Figures explained here: Figure 4, Figure 3 and Figure 1

    How counties are ranked and grouped

    A county's deprivation rank is the population-weighted mean of the Area Deprivation Index national ranks of its census tracts, weighted by 2019-2023 tract population; Connecticut tracts are assigned to the eight legacy counties.

    Deciles and quartiles hold equal numbers of the 578 large counties. Decile means are births-weighted means of county shares.

    Figures explained here: Figure 2 and Figure 4

    How uncertainty is measured

    Pooled WONDER shares carry Wilson score intervals on the counts. Decile and quartile means, pooled rates by mother's race, differences, ratios, correlations and slopes carry 95% percentile intervals from a bootstrap that resamples whole counties (2,000 draws, seed 12345); gaps between groups use the same draws for both groups.

    Withheld cells are excluded and never reconstructed

    WONDER withholds cells of 1 to 9 births. A withheld cell is missing: it leaves both the count below the cutoff and the denominator, which is the births in the published cells, and nothing is derived from the county totals.

    The birthweight cut has 11,250 withheld cells in these counties and the gestational-age cut 8,704; at 9 births each they could hold at most 0.5% and 0.4% of births.

    Four rankings of the same places

    The comparison follows the book's ranking switch rule, fixed on October 28, 2026 before any of these gradients was computed. The main gradient of the chapter is recomputed under four rankings of the same places, with the outcome, period, weights, bins and intervals unchanged: the published ADI; a standardized index that applies the ADI's coefficients to its measures after standardizing each one across tracts; median household income; and the share of adults 25 and older with a bachelor's degree or more. The three alternatives come from ACS tract estimates for 2019 to 2023, the period of the ADI.

    All four rankings use the same places, the 578 counties that have the outcome and all four rankings, so the ADI panel can differ slightly from the chapter's main figure. Tracts enter only if they have every input of the standardized index, which leaves out tracts without a median rent, home value or mortgage cost. A county takes the population-weighted mean of the ranks of its common-sample tracts, weighted by 2019-2023 tract population, with Connecticut tracts assigned to the eight legacy counties that WONDER uses.

    A pattern counts as changed when the worse end switches sides, when the two ends differ under one ranking and not the other, or when the rank correlation of bin order and bin mean falls on the other side of 0.9 and moves by at least 0.1.

    Figure explained here: Figure 5

    What these data cannot show

    The county figures describe places, and a county rate is an average over the births in it. A county ranked as least deprived can hold deprived neighborhoods, and the Area Deprivation Index understates deprivation in high-cost cities (Chapter 1.1, What the deprivation index measures (https://vishalsingh.org/zipcode/anatomy-of-deprivation)). A pattern across counties does not describe the babies in any one of them.

    The WONDER figures cover only counties of 100,000 or more residents, which hold 79.5% of births. Births in smaller counties are pooled by WONDER and cannot be placed on the deprivation scale, and the check against County Health Rankings shows that the pattern is less regular across all counties than across large ones.

    The sources differ in period and definition. The deprivation index draws on the American Community Survey for 2019 to 2023, while the births span 2018 to 2024. Rates by mother's race come from County Health Rankings for births in 2016 to 2022, for non-Hispanic Black, non-Hispanic white and Hispanic mothers, and they are pooled over the counties where a rate is published. Infant mortality by mother's race comes from 2018 and 2019 only, for single races of any ethnicity, so its white group includes Hispanic mothers and is not the group in the low-birthweight rates. The infant mortality county view covers only larger counties and leaves out county-years in which WONDER withholds the deaths, which are 13.6% of Black births and 5.2% of white births there. The intervals leave out those differences in source, period and group.

    Finally, none of these comparisons identifies a mechanism. Deprivation and race are tied to smoking, prenatal care, chronic stress, pollution, maternal age and education, and to the quality of the nearest hospital. Birthweight is associated with all of them. The two policy studies above are the only evidence in this chapter on what changes the numbers, and they speak to income and coverage, not to the rest. A county map cannot settle the mechanism behind any one county's rate or behind the gap between groups.

    References

    1. Almond, Douglas; Currie, Janet (2011). Killing Me Softly: The Fetal Origins Hypothesis. Journal of Economic Perspectives 25(3): 153-172. doi:10.1257/jep.25.3.153
    2. Aizer, Anna; Currie, Janet (2014). The Intergenerational Transmission of Inequality: Maternal Disadvantage and Health at Birth. Science 344(6186): 856-861. doi:10.1126/science.1251872
    3. Kind, Amy J. H.; Buckingham, William R. (2018). Making Neighborhood-Disadvantage Metrics Accessible: The Neighborhood Atlas. New England Journal of Medicine 378(26): 2456-2458. doi:10.1056/NEJMp1802313
    4. David, Richard J.; Collins, James W., Jr. (1997). Differing Birth Weight among Infants of U.S.-Born Blacks, African-Born Blacks, and U.S.-Born Whites. New England Journal of Medicine 337(17): 1209-1214. doi:10.1056/NEJM199710233371706
    5. Geronimus, Arline T. (1992). The Weathering Hypothesis and the Health of African-American Women and Infants: Evidence and Speculations. Ethnicity & Disease 2(3): 207-221.
    6. Hoynes, Hilary; Miller, Doug; Simon, David (2015). Income, the Earned Income Tax Credit, and Infant Health. American Economic Journal: Economic Policy 7(1): 172-211. doi:10.1257/pol.20120179
    7. Currie, Janet; Gruber, Jonathan (1996). Saving Babies: The Efficacy and Cost of Recent Changes in the Medicaid Eligibility of Pregnant Women. Journal of Political Economy 104(6): 1263-1296. doi:10.1086/262059

    Provenance

    Pipeline version
    0.1.0
    Build script
    book2/chapters/birthweight-and-preterm-birth/build.py (sha256 15908823ab9d370445413480d8ba74adfabfeb7a1e1ba498f748384d128e0e4e)
    Built on
    2026-10-07
    Site commit
    c2b1ff3309cb4a10833f884da91ac0057a66ad0a

    Inputs

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    data/staged/ses/acs5_tract2020_2019_2023.parquet7,232,4245fe6f730a35225f14d5d8abfc6b9bce58b52e545f309a7eac74f1dae74d7a31c7b4a2475b3852d3f91804716a04566ef8ceadacec2be9fb85f5eb642078efac6
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    Outputs

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    Machine formats