Pregnancy-specific influences on smoking behavior: Evidence from a within-person between-pregnancy analysis

INTRODUCTION: Pregnancy is associated with substantial reductions in cigarette smoking, yet the pregnancy-specific influences contributing to within-person differences in smoking behavior remain poorly understood. We examined whether pregnancy order and fetal sex were associated with smoking behavior across successive pregnancies within the same woman. METHODS: Participants were 120 multiparous smokers who reported smoking behavior before, during, and after 321 pregnancies in a discordant sibling prenatal tobacco exposure study. Mixed-effects Poisson and logistic regression models with pregnancies nested within mothers estimated associations of pregnancy order and fetal sex with smoking intensity and smoking cessation while adjusting for maternal age, education, race/ethnicity, and partner smoking. RESULTS: Women were more likely to quit smoking during the first trimester of their first pregnancy than during subsequent pregnancies (adjusted OR = 5.00, 95% CI 2.06-12.11), despite smoking more heavily before conception. Female fetal sex was associated with fewer cigarettes smoked during the first trimester (adjusted RR = 0.85, 95% CI 0.74-0.98), independent of maternal characteristics and pregnancy order. CONCLUSIONS: Pregnancy order and fetal sex were associated with meaningful within-person differences in smoking behavior across successive pregnancies. These findings identify pregnancy-specific influences on smoking behavior and establish a framework for future investigation of the mechanisms through which pregnancy naturally alters addictive behavior.