Fetal and Early-Life Antibiotics and Risk of Pediatric Inflammatory Bowel Disease: A Population-Based Nationwide Register Study.

Objective: To assess whether antibiotic exposure prenatally and before 2 years of age is associated with subsequent pediatric inflammatory bowel disease (PIBD), as earlier studies diverge substantially in risk estimations or do not include prenatal exposure. Methods: We performed a register-based cohort study including all children in Norway born 2004-2012 until study's end on December 31, 2020. Exposures were defined as dispensed antibiotics to mothers during pregnancy and to children before 2 years of age. Main outcome was Results: Among 536 819 children, 797 PIBD cases were identified. The aOR for developing PIBD if exposed to antibiotics before 2 years of age compared with no exposure was 1.33 (95% CI 1.15-1.53), adjusted for sex and prenatal antibiotic exposure. An adjustment for maternal smoking during pregnancy increased the aOR to 1.42 (1.22-1.66), but with minimal changes after further adjustments for potential confounders related to pregnancy, birth, or socioeconomic status. A dose-response association was observed in those receiving more than 2 antibiotic courses (aOR 1.47, 1.25-1.73), and with greater effect estimates for broad-spectrum antibiotics (aOR 2.57, 1.82-3.63). Antibiotic exposure during pregnancy was numerically but not significantly associated with offspring PIBD (aOR 1.15, 0.99-1.34). Conclusions: Children exposed to antibiotics before 2 years of age were more likely to develop pediatric IBD than controls. Exposure prenatally to maternal antibiotics was numerically but not statistically significant associated to subsequent PIBD.