Prenatal smoking cessation and the risk of delivering preterm and small-for-gestational-age newborns.

OBJECTIVE: To examine the association between prenatal smoking cessation and delivery of a preterm or small-for-gestational-age (SGA) newborn in a large U.S. subpopulation using the revised (2003) birth certificate, which now assesses maternal smoking status by trimester.

METHODS: We analyzed a cohort of U.S.-resident, singleton births in the 11 states that used the revised birth certificate in 2005 (n=915,441). Self-reported maternal smoking status was categorized as "never smoked," "quit in the first trimester," "quit in the second trimester," and "smoked throughout" pregnancy (referent). Multinomial logistic regression was used to estimate adjusted odds ratios (aORs) for three outcomes (preterm non-SGA, term SGA, or preterm SGA newborns) by maternal smoking status. Analyses stratified by maternal age were also conducted.

RESULTS: Compared with women who smoked throughout pregnancy, first-trimester quitters reduced their odds of delivering a preterm non-SGA newborn by 31% (aOR 0.69, 95% confidence interval [CI] 0.65-0.74), a term SGA newborn by 55% (aOR 0.45, 95% CI 0.42-0.48), and a preterm SGA newborn by 53% (aOR 0.47, 95% CI 0.40-0.55), similar to nonsmokers. Second-trimester quitters also reduced their odds of delivering preterm non-SGA and term SGA newborns but to a lesser magnitude. When comparing first-trimester quitters with smokers in each age group, older mothers had generally lower odds of these outcomes than younger mothers.

CONCLUSION: Pregnant smokers who quit in the first trimester lowered their risk of delivering preterm and SGA newborns to a level similar to that of pregnant nonsmokers, and this benefit appeared to increase with maternal age. These findings reinforce current clinical guidance to encourage smoking cessation among pregnant smokers and serve as an additional incentive to quit.

LEVEL OF EVIDENCE: II.