Oral contraceptive pill use before pregnancy and respiratory outcomes in early childhood.

Background: Oral contraceptive pills (OCPs) are often used soon before, and sometimes during, pregnancy. A few studies have suggested that OCP use before pregnancy may increase risks for childhood respiratory outcomes, but data are inconclusive. No studies have analyzed the two types of OCPs, estrogen-progestin combined pills and progestin-only pills, separately. Methods: In the Norwegian Mother and Child Cohort Study (MoBa), we prospectively examined associations of OCP use before pregnancy, by type, with lower respiratory tract infections in 60,225 children followed to 6 months old, lower respiratory tract infections and wheezing in 42,520 children followed to 18 months old, and asthma in 24,472 children followed to 36 months old. We used logistic regression to estimate odds ratios (ORs) and their 95% confidence intervals (CIs) crudely and with adjustment for a wide range of potential confounders. Result: Combined pills were used much more commonly than progestin-only pills. Taking combined pills before pregnancy was not associated with lower respiratory tract infections, wheezing, or asthma. Progestin-only pill use in the year before pregnancy had a slight positive association with wheezing at 6-8 months old [adjusted OR (95% CI) = 1.19 (1.05-1.34)]. Conclusion: Our finding that combined pill use before pregnancy was not related to respiratory outcomes should provide reassurance to the vast majority of mothers using OCPs before becoming pregnant. The small association with progestin-only pill use and early respiratory outcomes may reflect uncontrolled confounding or other bias. Nonetheless, it does suggest that these two types of pills should be examined separately in future analyses of respiratory and other childhood outcomes.