Antibacterial exposure during pregnancy and asthma diagnoses in childhood: findings from a Brazilian Birth Cohort.

Purpose: Evidence on the association of maternal use of antibacterials during pregnancy with childhood asthma remains inconsistent. Confounding or biases may jeopardize the association, thus hampering causal inference. We tested the hypothesis that maternal antibacterial use during pregnancy causally increases the risk of childhood asthma up to four years of age, with effect modification by mode of delivery, exclusive breastfeeding, postnatal antibacterial exposure, and lower respiratory tract infections (LRTI). Methods: We used data from the 2015 Pelotas Birth Cohort Study. Antibacterial use during pregnancy was collected from self-reports. Information on child asthma was obtained from maternal reports of the child’s asthma diagnosis. We performed a double-bias adjustment using multivariable Logistic regression after inverse probability of treatment weighting. Effect modification by mode of delivery, exclusive breastfeeding, postnatal antibacterial exposure, and child lower respiratory tract infections were investigated. Progestogens used during pregnancy were assessed as an exposure negative control. Results: The analytical sample included 3942 children. The prevalence of asthma diagnosis was 10.6% (95% CI 9.7-11.6). There was no evidence of a causal effect of maternal antibacterial use during pregnancy on asthma at age 4. There was evidence of an effect among those who did not use postnatal antibacterials. We found no evidence of a causal effect in the negative control analysis. Conclusion: We observed no association between the use of antibacterials during pregnancy and asthma up to age 4. In the main analysis, there was evidence of effect modification by postnatal antibacterials, which was absent in the negative control analysis.