Smoking Cessation and Pregnancy: Timing of Cessation Reduces or Eliminates the Effect on Low Birth Weight.

Background: Women who smoke cigarettes while pregnant are at elevated risk of having low birth weight infants (LBW, < 2500 g) which increases risks of infant mortality and morbidity, including chronic conditions later in life.

Objective: Smoking cessation during pregnancy can reduce the risk of poor birth outcomes. However, the effect that timing of smoking cessation has on the reduction of poor birth outcomes in term pregnancies is unknown.

Study Design: This retrospective cohort study used birth certificate data from Missouri singleton, full-term, live births from 2010 to 2012 (N = 179,653) to examine the rates and timing of smoking cessation during pregnancy on birthweight. Smoking exposure was categorized as non-smoker, preconception cessation, first trimester cessation, second trimester cessation, and smoker. The outcome was low birth weight (LBW). Covariates included maternal race/ethnicity, age, education level, type of payment for the delivery, marital status, paternal acknowledgement, prenatal sexually transmitted infection (STI), comorbidities, and body mass index. Bivariate and multivariable analyses were used to assess relationships between smoking and LBW status.

Results: Preconception cessation did not have a statistically higher risk for LBW than mothers who never smoked (aOR 1.12; 95% CI 0.98, 1.28). First trimester cessation (aOR 1.26; 95% CI 1.05, 1.52), second trimester cessation (aOR 2.00; 95% CI 1.60, 2.67), and smoker (aOR 2.46; 95% CI 2.28, 2.67) had increasing odds for LBW relative to mothers who did not smoke. All covariates had significant relationships with the smoking exposure.

Conclusion: Preconception cessation yielded LBW rates comparable to non-smokers. The risk for LBW increased as smoking continued throughout pregnancy among full term births, an important new finding in contrast with other studies.