Influence of antibiotics given during labour and birth on body mass index z scores in children in the All Our Families pregnancy cohort

Summary Background/objectives Little is known about obesity risk associated with intrapartum antibiotic prophylaxis (IAP). Our objective was to determine if maternal antibiotic exposure during birth is associated with child body mass index (BMI) z scores in the first 3 years of life. Methods In 2008 to 2010, 3388 pregnant women were recruited to the All Our Families study. Here, we included women with available data from obstetrical records on antibiotic use during birth (n = 1303) and children with at least one valid BMI z score (final sample n = 1262). The primary outcome was infant BMI z score at 1, 2 and 3 years of age. Results IAP occurred in 432 of 1262 women. Children exposed to IAP had significantly higher mean [standard error (SE)] BMI z scores (1.071 [0.087] unit) at 1 year of age compared to non‐exposed infants (0.744 [0.064] unit). Although the association was no longer significant after adjustment for confounding factors in the growth trajectory model, IAP resulted in a 0.255 unit increase in BMI z score at 1 year of age. Differences in BMI z score between exposed and non‐exposed at baseline (year 1) only remained significant in sensitivity analysis. Conclusion The potential association between maternal IAP and increased infant BMI z score at 1 year of age should be confirmed in other cohorts and warrants investigation of interventions to mitigate this possible risk.