Maternal Analgesic Exposure and Fetal Ductal Constriction: A Prospective Cohort Study in Late Pregnancy.

Maternal exposure to analgesics in late pregnancy was associated with fetal ductal constriction compared with unexposed controls. The association was stronger for metamizole and consistent with a dose-related pattern. Acetaminophen was associated with mild, reversible ductal involvement in a subset of fetuses. Reversibility after drug withdrawal supports a functional, prostaglandin-mediated mechanism. These findings have important implications for maternal analgesic use in late gestation and highlight the value of Doppler surveillance following exposure to prostaglandin-modulating agents.