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

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.