Chapter 2.3 · Before the first breath

Smoking in pregnancy

In large counties with a usable count, the share of births to mothers who reported smoking fell from 5.4% in 2018 to 1.9% in 2024 and stayed higher where county income was lower.

Author: Vishal Singh
Affiliation: NYU Stern
Published: 9 October 2026

In 2018, 5.4% of births with a known answer in the large American counties studied here were to mothers who reported smoking during pregnancy, and in 2024 the share was 1.9%. A large county is one of 100,000 residents or more, the size at which the CDC WONDER birth records name a county on its own. The answer comes from the birth certificate, which records whether the mother used tobacco while pregnant. The chapter follows the 530 such counties outside California that publish a smoking count in every year from 2018 to 2024. In every one of those years, the share was higher in counties with lower median household income.

Smoking fell in every county income group

The chapter ranks these counties on median household income and splits them into thirds that hold equal numbers of counties. A third's smoking share pools its births, counting the births to mothers who reported smoking over the births with a known answer. It therefore describes counties and groups of births, not individual mothers.

The share fell in every third in every year, and the thirds kept their order throughout, with intervals that never overlap. The lowest-income third had the highest share and the highest-income third the lowest. In 2018 the lowest-income third exceeded the highest-income third by 4.6 (95% CI 3.6 to 5.6) points.

Figure 1

Smoking in pregnancy fell from 8.2% to 3.3% of births in the lowest-income third of large counties and from 3.6% to 1.1% in the highest-income third

Share of births to mothers who reported smoking, among births with a known tobacco answer, by third of the 530 large counties ranked on median household income, 2018 to 2024, with 95% intervals from a bootstrap over counties

Mothers who reported smoking (% of births with a known answer)

Show data

Data for Smoking in pregnancy fell from 8.2% to 3.3% of births in the lowest-income third of large counties and from 3.6% to 1.1% in the highest-income third
conf_high	conf_low	n	series	share	year
9.17	7.31	603,928	Lowest-income third	8.18	2018
8.45	6.75	599,484	Lowest-income third	7.56	2019
7.99	6.34	580,344	Lowest-income third	7.14	2020
6.75	5.32	579,539	Lowest-income third	6.01	2021
5.43	4.26	579,736	Lowest-income third	4.81	2022
4.49	3.51	567,037	Lowest-income third	3.97	2023
3.71	2.89	567,610	Lowest-income third	3.27	2024
6.73	4.42	938,985	Middle third	5.47	2018
6.17	4.04	924,476	Middle third	5	2019
5.63	3.70	890,673	Middle third	4.58	2020
4.59	2.99	899,921	Middle third	3.72	2021
3.66	2.37	906,572	Middle third	2.96	2022
2.91	1.89	890,288	Middle third	2.36	2023
2.32	1.52	894,429	Middle third	1.89	2024
4.04	3.22	968,024	Highest-income third	3.61	2018
3.60	2.85	959,133	Highest-income third	3.21	2019
3.23	2.56	932,668	Highest-income third	2.88	2020
2.58	2.05	960,611	Highest-income third	2.30	2021
1.98	1.57	962,137	Highest-income third	1.76	2022
1.65	1.29	946,374	Highest-income third	1.46	2023
1.28	0.990	961,896	Highest-income third	1.13	2024
5.91	4.88	2,510,937	All large counties	5.40	2018
5.41	4.45	2,483,093	All large counties	4.93	2019
5	4.09	2,403,685	All large counties	4.54	2020
4.08	3.34	2,440,071	All large counties	3.71	2021
3.23	2.63	2,448,445	All large counties	2.93	2022
2.64	2.14	2,403,699	All large counties	2.38	2023
2.11	1.72	2,423,935	All large counties	1.91	2024

Every line falls in every year, and the lowest-income third stays on top of the highest-income third, with bands that do not overlap in any year. Each line is the pooled share of births to mothers who reported smoking in the large counties of its income group, with counties ranked on median household income for 2022. The middle third and the line for all large counties are drawn in grey. Values in Table 1.

Note: Large counties are the counties that CDC WONDER names individually: those with 100,000 residents or more. WONDER pools the births of every smaller county in a state into one row, so smaller counties are not in these data. Of the 578 large counties named in every year from 2018 to 2024, California (35) and 13 counties with a withheld smoking count are left out, which leaves 530.Note: A county's smoking share is the births to mothers who reported smoking over the births with a known answer, Yes plus No. Births with an Unknown or Not Stated answer are left out of the denominator.Note: County median household income is the County Health Rankings 2024 release, a Census Small Area Income and Poverty Estimates value for 2022. Its year differs from the births, which are from 2018 to 2024. Thirds hold equal numbers of counties.Note: Intervals are 95% intervals from a bootstrap over counties (replicates and seed in the methods note). Births are full counts, so an interval shows how much a pooled share depends on which counties are in the group.Source: CDC WONDER natality, tobacco use during pregnancy, births in 2018-2024; full counts of births; counties ranked on County Health Rankings 2024 median household income (Census SAIPE 2022); intervals from a bootstrap over counties

How we know

The counts are births from CDC WONDER natality for 2018 to 2024, by the mother's county of residence and her answer to the tobacco item. WONDER pools the births of every smaller county in a state into one row, so those counties cannot be placed on an income scale. The counties used hold 66.9% of the births in the United States in those years. California is left out because WONDER's documentation says it does not collect the item routinely. County income is a Census estimate for 2022, taken from County Health Rankings, so its year differs from the births. WONDER withholds a county's smoking count in any year with fewer than 10 smoking births, and the chapter keeps a county only if its count is published in every year. That rule leaves out 13 counties. It selects on the outcome, and the counties it removes are affluent. Among them are Arlington, Fairfax, Loudoun and Alexandria in Virginia. Suppose each withheld cell in the high-income counties held one birth fewer than the withholding floor, a limit and not a value for any cell. Those cells could then add at most 0.17% to the smoking births of the highest-income third. The report gives every estimate with its interval and sample size.

Within states the gradient holds, but weighting changes its size

A difference across all counties could come from comparing states that differ in both income and smoking. The chapter therefore also compares counties only inside the same state, with a fixed-effects slope that gives each state its own baseline. For births pooled over 2018 to 2024, each doubling of county median household income goes with a smoking share 3.9 (95% CI 2.7 to 5.5) points lower when counties are weighted by their births. When each county counts once, the share is 6.6 (95% CI 5.1 to 8.2) points lower. Under either weighting, the slope inside states differs from the slope across the counties of the same states by an amount whose interval includes zero. The gap between higher-income and lower-income counties therefore appears inside states about as it appears across them. A weighted slope leans on the counties with more births than the median county, where the gradient is shallower in points.

States with at least 8 of these counties get a line of their own (Figure 2). In all 26 of them the estimated slope is below zero. When counties are weighted by births, the interval lies wholly below zero in 10 states and wholly above zero in none. The intervals are wide because each line rests on one state's large counties, which in a typical state differ by less than a doubling of income.

Figure 2

In all 26 states with a slope of their own the estimated slope is below zero, and the 95% interval lies below zero in 10 when counties are weighted by births

Change in the share of births to mothers who smoked per doubling of county median household income (SAIPE 2022), one dot per state with at least 8 complete large counties, 2018 to 2024, with 95% intervals; four views by scale and by weighting

Interval includes zero
Interval below zero

Show data

Data for In all 26 states with a slope of their own the estimated slope is below zero, and the 95% interval lies below zero in 10 when counties are weighted by births, Points, weighted by births
State	Scale	Counties	Slope	Lower limit of the 95% interval	Upper limit of the 95% interval	Complete counties	Counties left out for a withheld count	State share (%)
Alabama	points	Weighted by births	−3.28	−7.14	0.58	12	0	4.6
Arizona	points	Weighted by births	−4.97	−13.64	3.70	9	0	3.2
Colorado	points	Weighted by births	−4.35	−8.56	−0.14	11	0	3.7
Connecticut	points	Weighted by births	−6.42	−16.92	4.08	8	0	2.6
Florida	points	Weighted by births	−3.97	−10.03	2.09	32	1	2.7
Georgia	points	Weighted by births	−3.34	−4.95	−1.73	22	2	1.8
Illinois	points	Weighted by births	−8.37	−16.40	−0.33	19	1	2.9
Indiana	points	Weighted by births	−7.17	−10.21	−4.12	17	0	6.7
Louisiana	points	Weighted by births	−0.81	−6.94	5.31	14	0	3.1
Maryland	points	Weighted by births	−4.04	−9.51	1.43	13	0	3.1
Massachusetts	points	Weighted by births	−4.24	−7.52	−0.97	11	0	2.8
Michigan	points	Weighted by births	−7.45	−24.40	9.51	20	0	6.6
Minnesota	points	Weighted by births	−7.80	−19.54	3.93	10	0	3.7
Missouri	points	Weighted by births	−6.23	−12.12	−0.34	10	0	7.2
New Jersey	points	Weighted by births	−1.86	−4.47	0.75	19	0	1.9
New York	points	Weighted by births	−2.36	−9.13	4.41	27	1	2.3
North Carolina	points	Weighted by births	−8.20	−11.15	−5.25	27	0	4.2
Ohio	points	Weighted by births	−7.34	−13.71	−0.98	28	0	8.3
Oregon	points	Weighted by births	−9.98	−15.26	−4.70	9	0	4.8
Pennsylvania	points	Weighted by births	−5.10	−15.68	5.47	31	0	6.4
South Carolina	points	Weighted by births	−4.51	−10.99	1.97	15	0	4.5
Tennessee	points	Weighted by births	−0.91	−28.66	26.85	11	1	5.5
Texas	points	Weighted by births	−0.63	−2.10	0.83	36	3	1.3
Virginia	points	Weighted by births	−2.72	−5.20	−0.25	11	4	2.8
Washington	points	Weighted by births	−5.69	−14.20	2.83	12	0	3.7
Wisconsin	points	Weighted by births	−3.37	−20.54	13.80	15	0	5.5

Every dot is left of zero in the first view. The intervals are wide; those for some states lie wholly left of zero, the rest cross zero, and none lies right of it. Each dot is a least-squares line through one state's large counties, in points of the smoking share per doubling of county income with counties weighted by births. The vertical rule marks the common slope across these states. The other views count each county once or give the slope in proportion to the share. Rows are ordered by the estimate only to make the figure readable, and the order is not a ranking. Values in Table 5.

Note: Large counties are the counties that CDC WONDER names individually: those with 100,000 residents or more. WONDER pools the births of every smaller county in a state into one row, so smaller counties are not in these data. Of the 578 large counties named in every year from 2018 to 2024, California (35) and 13 counties with a withheld smoking count are left out, which leaves 530.Note: County median household income is the County Health Rankings 2024 release, a Census Small Area Income and Poverty Estimates value for 2022. Its year differs from the births, which are from 2018 to 2024.Note: A state gets a slope when it has at least 8 complete counties, which gives 26 states and 449 counties. Intervals are 95% intervals from a t distribution with the state's counties minus two degrees of freedom and heteroskedasticity-robust (HC3) standard errors, so a state with few counties has a wide interval and the interval may be too narrow where one county dominates.Note: Virginia has 4 of its 15 large counties left out for a withheld smoking count, and counties left out in other states are listed in the data table. A state with counties left out rests on the rest.Note: Counties differ by less than a doubling of income in a typical state: the median span between a state's lowest and highest county income is 0.9 doublings, so the slopes extend beyond what most states' own counties cover.Source: CDC WONDER natality, tobacco use during pregnancy, births in 2018-2024; full counts of births; counties ranked on County Health Rankings 2024 median household income (Census SAIPE 2022); state slopes weighted by births with a known answer or unweighted as labeled, 95% t intervals

Whether the slope is the same in every state depends on the weights and on the scale. Of the chapter's tests of equal state slopes, only the test in points with each county counting once finds that they differ. It does so at every minimum number of counties per state that the chapter tries except the lowest, 3. In points, the steeper slopes belong to states with more smoking. In proportion to the share, the correlation between a state's slope and its smoking level has an interval that includes zero.

The gap shrank in points and grew in proportion

Falling levels change how a gap reads. The difference between the lowest-income and highest-income thirds narrowed from 4.6 points in 2018 to 2.1 (95% CI 1.7 to 2.6) points in 2024. Over the same years, the ratio of their shares rose from 2.3 (95% CI 1.9 to 2.7) to 2.9 (95% CI 2.4 to 3.5). A gap in points shrinks when the level falls even if the proportional difference stays the same. Here the proportional difference grew, and smoking fell faster in proportion where county income is higher. The within-state slope, measured year by year for the same counties, shows the same split (Figure 3).

Figure 3

The within-state slope in points shrank from 4.9 to 2.4 points per doubling of county income from 2018 to 2024 while the slope in proportion grew from 10.1% to 14.7%

Within-state slope of the smoking share on county median household income (SAIPE 2022), by year of birth, 2018 to 2024, in percentage points per doubling of income or as a percent difference per 10% higher income, with 95% intervals from a bootstrap over states

Percentage points per doubling of county median household income

Show data

Data for The within-state slope in points shrank from 4.9 to 2.4 points per doubling of county income from 2018 to 2024 while the slope in proportion grew from 10.1% to 14.7%, Percentage points per doubling
conf_high	conf_low	measure	n	slope	year
−3.45	−6.98	points	45	−4.89	2018
−3.31	−6.71	points	45	−4.70	2019
−3.25	−6.62	points	45	−4.65	2020
−2.80	−5.76	points	45	−4.02	2021
−2.32	−4.78	points	45	−3.31	2022
−1.99	−4.03	points	45	−2.81	2023
−1.70	−3.36	points	45	−2.39	2024

In the first view the line climbs toward zero each year as smoking falls, and in the second it falls each year, so the gradient flattens in points and steepens in proportion. Each point is the within-state slope for one year of births, with counties weighted by their births with a known answer and the same counties in every year. Values in Table 8.

Note: Large counties are the counties that CDC WONDER names individually: those with 100,000 residents or more. WONDER pools the births of every smaller county in a state into one row, so smaller counties are not in these data. Of the 578 large counties named in every year from 2018 to 2024, California (35) and 13 counties with a withheld smoking count are left out, which leaves 530.Note: County median household income is the County Health Rankings 2024 release, a Census Small Area Income and Poverty Estimates value for 2022. Its year differs from the births, which are from 2018 to 2024.Note: Intervals are 95% intervals from a bootstrap over states (replicates and seed in the methods note), which allows for counties in one state resembling each other. The same counties are used in every year, and each is published in every year.Note: The slopes are negative: a value farther below zero means a lower smoking share for a doubling of county income.Source: CDC WONDER natality, tobacco use during pregnancy, births in 2018-2024; full counts of births; counties ranked on County Health Rankings 2024 median household income (Census SAIPE 2022); slopes weighted by births with a known answer, intervals from a bootstrap over states

A narrower gap in points therefore does not mean that the proportional difference between lower-income and higher-income counties shrank. These are patterns among places. A county with higher median household income has a lower smoking share, and that says nothing about the income of the mothers who smoked, which these data do not hold. The pattern is ecological and need not hold for the mothers inside the counties. The studies of state policy that the report describes bear on what changes smoking in pregnancy, and neither measures the county gradient. Lien and Evans found that smoking participation among pregnant women fell in states that adopted large cigarette tax increases, relative to matched control states.[1] The weight of the babies born to these mothers is the subject of Chapter 2.1, Birthweight and preterm birth, and smoking among adults is the subject of Chapter 7.2, Health behaviors, person by person.

What this cannot tell you

The item is reported at birth, so the fall in the share can reflect less smoking, a change in how or whether the item is recorded, or a change in who gives birth. These data cannot separate them, and the item is named tobacco use and may include products other than cigarettes. Smaller counties are not in these data, so the chapter says nothing about them, and a county's 2022 income stands in for its income in earlier years. None of this identifies why smoking is less common where incomes are higher.

Go deeper

The report: every estimate with its interval and sample size.
Tables: every figure of the report as a table.

Data sources

CDC WONDER natalityCDC WONDER natality, county by tobacco use during pregnancy and county totals, births in 2018 to 2024 (consolidated pulls); 2024 is finalYears: 2018-2024 · Weights: none (full counts of births); shares pooled over counties, births-weighted or unweighted as stated · License: Public domain (NCHS, CDC); WONDER data-use restrictions apply
County Health RankingsCounty Health Rankings 2024 release, median household income (Census Small Area Income and Poverty Estimates, 2022)Years: 2024 release · Weights: none (published county values) · License: CC BY 4.0 (University of Wisconsin Population Health Institute)
Area Deprivation IndexNeighborhood Atlas Area Deprivation Index 2023 (v4.0.1), tract national rank, averaged to counties with 2019-2023 tract population; used as a check on the income measureYears: 2023 release (version 4.0.1; built on ACS 2019-2023) · Weights: 2019-2023 tract population · License: Free for non-commercial use; cite the Neighborhood Atlas and Kind and Buckingham
Published estimates from cited studiesFindings of two studies of state policy and maternal smoking: the abstract of Lien and Evans (2005) and Table 2 of Markowitz and coauthors (2017)Years: as reported in each study · Weights: not applicable · License: Quoted from published research for commentary

All data sources

References

Lien, Diana S.; Evans, William N. (2005). Estimating the Impact of Large Cigarette Tax Hikes: The Case of Maternal Smoking and Infant Birth Weight. Journal of Human Resources 40(2): 373-392. doi:10.3368/jhr.xl.2.373

How to cite

@misc{singh2026smokinginpregnancy,
  author = {Singh, Vishal},
  title = {Smoking in pregnancy},
  year = {2026},
  url = {https://vishalsingh.org/zipcode/smoking-in-pregnancy},
  note = {In ZIP Code Destiny. Published 9 October 2026.}
}