Prenatal antibiotic exposure and childhood asthma: a population-based study.

Antibiotic use during infancy alters gut microbiota and immune development and is associated with an increased risk of childhood asthma. The impact of prenatal antibiotic exposure is unclear. We sought to characterise the association between prenatal antibiotic exposure and childhood asthma.We performed a population-based cohort study using prescription records, hospitalisation records and physician billing claims from 213 661 mother-child dyads born in Manitoba, Canada between 1996 and 2012. Associations were determined using Cox regression, adjusting for maternal asthma, postnatal antibiotics and other potential confounders. Sensitivity analyses evaluated maternal antibiotic use before and after pregnancy.36.8% of children were exposed prenatally to antibiotics and 10.1% developed asthma. Prenatal antibiotic exposure was associated with an increased risk of asthma (adjusted hazard ratio (aHR) 1.23, 95% CI 1.20-1.27). There was an apparent dose response (aHR 1.15, 95% CI 1.11-1.18 for one course; aHR 1.26, 95% CI 1.21-1.32 for two courses; and aHR 1.51, 95% CI 1.44-1.59 for three or more courses). Maternal antibiotic use during 9 months before pregnancy (aHR 1.27, 95% CI 1.24-1.31) and 9 months postpartum (aHR 1.32, 95% CI 1.28-1.36) were similarly associated with asthma.Prenatal antibiotic exposure was associated with a dose-dependent increase in asthma risk. However, similar associations were observed for maternal antibiotic use before and after pregnancy, suggesting the association is either not directly causal, or not specific to pregnancy.
Competing Interests: Conflict of interest: M.B. Azad reports grants (unrestricted research grants) from Heart and Stroke Foundation of Canada/Canadian Lung Association /Canadian Respiratory Research Network/Allergy, Genes and Environment Network of Centres of Excellence (co-funders), and from Children's Hospital Foundation of Manitoba, during the conduct of the study. Conflict of interest: S.M. Mahmud reports grants (unrestricted research grants) from GlaxoSmithKline, Sanofi Pasteur, Pfizer, Merck and Roche, outside the submitted work.
(Copyright ©ERS 2018.)