Maternal Cigarette Smoking Trajectories and Risk of Low Birthweight in the United States: A Population-Based Analysis of 2023 to 2024 Natality Data

Background

Maternal cigarette smoking is associated with adverse birth outcomes, but low birthweight may reflect preterm delivery, restricted fetal growth, or both. Contemporary evidence distinguishing smoking trajectories is limited.

Objectives

To examine associations between maternal cigarette-smoking trajectories and low birthweight among U.S.-resident singleton live births in 2023 to 2024.

Methods

We analysed 5,861,166 U.S.-resident singleton live births in the 2023 to 2024 National Vital Statistics System natality files. Low birthweight was defined as birthweight <2,500 g. Trajectories were never smoking, quitting before pregnancy, quitting during pregnancy, persistent smoking, or other/intermittent smoking. Modified Poisson regression estimated adjusted risk ratios (aRRs) and 95% confidence intervals controlling for birth year and maternal, pregnancy, and infant characteristics.

Results

Low-birthweight prevalence was 6.4% among never smokers, 7.7% among mothers who quit before pregnancy, 11.2% among those who quit during pregnancy, 14.6% among persistent smokers, and 10.2% among those with other/intermittent smoking. Compared with never smoking, adjusted risks were higher for quitting before pregnancy (aRR 1.06, 95% CI 1.03, 1.09), quitting during pregnancy (aRR 1.46, 95% CI 1.42, 1.51), persistent smoking (aRR 1.95, 95% CI 1.93, 1.98), and other/intermittent smoking (aRR 1.36, 95% CI 1.25, 1.49). Associations varied little by year (joint interaction P = 0.102).

Conclusions

Persistent smoking showed the strongest association with low birthweight. Because the outcome combines preterm delivery and impaired fetal growth, the estimates should not be interpreted as associations with fetal growth restriction alone.

Synopsis

Study question

How are maternal cigarette-smoking trajectories before and during pregnancy associated with low birthweight among U.S.-resident singleton live births in 2023–2024?

What’s already known

Maternal smoking during pregnancy is associated with low birthweight, and earlier smoking cessation is generally associated with more favourable birth outcomes.²–

What this study adds

Among 5,861,166 births, persistent smoking showed the strongest association with low birthweight (aRR 1.95, 95% CI 1.93, 1.98), followed by quitting during pregnancy (aRR 1.46, 95% CI 1.42, 1.51). Quitting before pregnancy showed only a small residual association (aRR 1.06, 95% CI 1.03, 1.09). Findings were consistent across 2023–2024 and support distinguishing smoking trajectories rather than using a simple binary exposure.