Modifying the risk of recurrent preterm birth: influence of trimester-specific changes in smoking behaviors.

BACKGROUND

Women with at least 1 prior occurrence of premature birth often have demographic and medical risk factors that are not modifiable. However, smoking cessation could be a targeted intervention in which a woman with a history of premature birth may be able to reduce her future risk of recurrence.

OBJECTIVE

This study aims to assess how trimester-specific smoking patterns influence the risk of recurrent premature birth.

STUDY DESIGN

This was a population-based retrospective cohort study of singleton nonanomalous live births in Ohio, 2006-2012 using vital statistics birth records. This analysis was limited to women with at least 1 prior premature birth. Rates of birth <37 weeks were compared among nonsmokers, women who smoked in the 3 months prior to pregnancy and quit in the first vs quit in the second vs quit in the third trimester. Multivariate logistic regression analyses assessed the association between smoking cessation at various time points in pregnancy and recurrent premature birth while adjusting for maternal race, education, Medicaid enrollment, and marital status.

RESULTS

We analyzed the outcomes of 36,432 women with a prior premature birth who subsequently delivered at 20-42 weeks. One third of women with a prior premature birth smoked during pregnancy. Of smokers, 16% quit early in the first trimester, 7% quit in the second, 5% quit in the third trimester, and 72% smoked throughout pregnancy. The rate of recurrent premature birth in nonsmokers was high 28% in this cohort. Smoking in pregnancy with cessation in the first or second trimester was not significantly associated with an increase in recurrent premature birth rates (first trimester, 29% adjusted odds ratio, 0.97 [95% confidence interval, 0.9-1.1], and second trimester, 31% adjusted odds ratio, 1.10 [95% confidence interval, 0.9-1.3], respectively). However, quitting late in pregnancy (third trimester) was associated with a high rate (43%) of delivery <37 weeks, adjusted odds ratio, 1.81 (95% confidence interval, 1.48-2.21). Continued smoking throughout pregnancy was also associated with an increased recurrent premature birth (32%), adjusted odds ratio, 1.14 (95% confidence interval, 1.07-1.22), despite adjustment for concomitant premature birth risk factors.

CONCLUSION

Smoking cessation in pregnancy and its relationship to preterm birth has been studied extensively, and it is widely accepted that smoking in pregnancy increases preterm birth rates. However, this study provides novel information quantifying the risk of recurrent preterm birth and stratifies the increased risk of recurrent preterm birth by trimester-specific smoking behavior. Although women with even 1 prior premature birth are at an inherently high risk of recurrence, women who stopped smoking early in the first 2 trimesters experienced similar preterm birth rates compared with nonsmokers. However, delayed smoking cessation or smoking throughout pregnancy significantly increased recurrent premature birth risk. Smoking cessation is a potential modifiable risk factor for recurrent preterm birth in high-risk pregnancies. This study highlights the importance of early pregnancy smoking cessation in those at especially high risk, women with a prior preterm birth.