Does antimicrobial use during pregnancy impact excess weight in early childhood? Findings from the 2015 Pelotas (Brazil) Birth Cohort Study

Abstract Background: Studies have suggested that prenatal exposure to antimicrobials might be associated with obesity during childhood. Objective: This study aimed to investigate the association between the use of antimicrobials during pregnancy and excess weight in children at ages three, 12, 24 and 48 months. Methods: Data of participants from the 2015 Pelotas (Brazil) Birth Cohort study were analyzed (N=4,275). The use of antimicrobials during pregnancy was assessed using standardized questionnaires and excess weight was defined as BMI for age in z-score ≥ 1. Results: Over 43% of women used at least one antimicrobial during pregnancy. The proportion of children with excess weight increased from 17.6% (95%CI 16.5; 18.8) at age 3mo to 43.8% (95%CI 42.2; 45.4) at age 48mo. Overall, most associations investigated between the use of antimicrobials during pregnancy and excess weight in children were null. The use of antimicrobials during the second trimester of pregnancy was associated with lower BMI-for-age at three months. On average, children whose mothers used antimicrobials in one trimester of pregnancy had a BMI-for-age at 12mo 0.11 z-score (95%CI 0.01; 0.20) higher than those from mothers who did not use antimicrobials. An increased risk in excess weight at 48mo [RR= 1.13 (95%CI 1.04; 1.23)] was observed among children whose mothers’ used antimicrobials in the first trimester of pregnancy. Conclusion: Given that most of the associations investigated had either null results or a small magnitude of association, this study does not support previous findings that the use of antimicrobial during pregnancy impacts excess weight in early childhood.