Background Maternal asthma during pregnancy is associated with an increased risk of bronchiolitis and asthma in offspring, but the mechanisms remain poorly understood. We aimed to assess whether impaired postnatal infant lung function independently influences the risk of bronchiolitis and asthma in childhood or whether it mediates the association between maternal asthma during pregnancy and respiratory outcomes. Methods We analysed harmonised infant lung function data from two birth cohorts: the Australian Breathing for Life Trial and the Swiss Basel-Bern Infant Lung Development. Bronchiolitis hospitalisation (verified through medical records) and asthma at age six (parent-reported) were primary outcomes. Lung function measured included the ratio of maximum tidal inspiratory flow to maximum tidal expiratory flow (MTIF/MTEF) and the time to peak tidal expiratory flow to total expiratory time ratio, tPTEF/tE. Multivariable logistic regression assessed associations, and generalised structural equation modelling was used for mediation analyses. Results The study included 1203 term infants with 89 cases of bronchiolitis hospitalisation. Tidal breathing lung function ratios were associated with bronchiolitis hospitalisations: MTIF/MTEF adjusted ORs (aORs) 2.90, 95% CI 1.20 to 7.02, p=0.018; asthma in childhood: tPTEF/tE aOR 0.97, 95% CI 0.94 to 0.99, p=0.013 and MTIF/MTEF aOR 2.94, 95% CI 1.07 to 8.02, p=0.036. MTIF/MTEF ratio mediated 11% of the total effect of asthma during pregnancy on bronchiolitis risk, and MTIF/MTEF and tPTEF/tE ratios mediated 3% of the effect of asthma during pregnancy on childhood asthma risk. Conclusion Postnatal lung function was associated with subsequent bronchiolitis and childhood asthma. Additionally, the effect of maternal asthma during pregnancy on the outcomes was partially mediated by impaired lung function.
Sena et al. (Fri,) studied this question.