Wang B, et al. - Researchers used a multi-center prospective cohort of the U.S. Collaborative Perinatal Project (1959-1976) to study the link between fetal exposure to antibiotics and obesity at ages 4 and 7 years among 43,332 children, given mounting evidence has linked postnatal antibiotic use with body mass index (BMI) in children. They estimated risk ratios (RRs) of obesity (BMI > 95th percentile) by using modified Poisson regression models. The association with BMI Z-score was evaluated using linear mixed models. Findings revealed an increased risk of mid-childhood obesity related to repeated use of antibiotics during pregnancy; for repeated exposures in the second trimester, the strongest magnitude of association was reported. No association of prenatal antibiotic use with obesity or BMI z-score at age 4 years was found.