Examining the role of pre‐pregnancy weight and gestational weight gain in allergic disease development among offspring: A population‐based cohort study in Ontario, Canada

BACKGROUND: Studies suggest maternal weight and weight gain during pregnancy may influence foetal immunological development. However, their role in the aetiology of allergic disease is unclear. OBJECTIVES: We sought to examine the impact of maternal pre‐pregnancy body mass index (BMI) and gestational weight gain (GWG) on the incidence of four common paediatric allergic diseases. METHODS: We conducted a retrospective, population‐based cohort study of all singleton live births in Ontario, Canada between 2012 and 2014, using maternal‐newborn records from the provincial birth registry linked with health administrative databases. Neonates were followed up to 7 years for anaphylaxis, asthma, dermatitis and rhinitis, identified through validated algorithms based on healthcare encounters. We multiply imputed missing data and employed Cox proportional‐hazards models to calculate adjusted hazard ratios (aHR) with 95% confidence intervals (CI). To test the robustness of our findings, we also conducted several sensitivity analyses, including probabilistic bias analyses for exposure and outcome misclassification. All methods were prespecified in a published protocol. RESULTS: Of the 248,017 infants followed, 52% were born to mothers with a pre‐pregnancy BMI in the normal range and only 19% were born to mothers with adequate weight gain during pregnancy. Incidence rates (per 100,000 person‐days) for anaphylaxis, asthma, dermatitis and rhinitis were 0.22, 6.80, 12.41 and 1.54, respectively. Compared with normal BMI, maternal obesity was associated with increased hazards of asthma in offspring (aHR 1.08, 95% CI 1.05, 1.11), but decreased hazards of anaphylaxis (aHR 0.83, 95% CI 0.69, 0.99) and dermatitis (aHR 0.97, 95% CI 0.94, 0.99). In contrast, maternal underweight was associated with increased hazards of dermatitis (aHR 1.06, 95% CI 1.02, 1.10). We found no associations between pre‐pregnancy BMI and rhinitis or GWG and any allergic outcome, and no evidence of effect measures modification by infant sex. CONCLUSIONS: These findings provide support for the involvement of maternal pre‐pregnancy BMI in paediatric allergic disease development.