Do Antibiotics Increase Risk for Pregnancy in Oral Contraceptive Users?

Despite a lack of credible evidence supporting the belief that antibiotic use (other than rifampin) is linked to combined oral contraceptive (OC) failure, package inserts for both products warn of potential interactions. Investigators examined this risk using data from two national birth defect surveillance programs involving nearly 44,000 women; 1330 women reported an unplanned pregnancy and OC use for at least 1 month before and part of the month after conception (cases). Cases served as their own controls to derive self-matched odds ratios (ORs) by comparing antibiotic use during the 4 weeks before conception (case period, when antibiotics might be most likely to affect pregnancy risk) with use during the 4 to 8 weeks before conception (…