No obvious impact of caesarean delivery on childhood allergic outcomes: findings from Australian cohorts.

Background and Objective: As caesarean delivery and childhood allergy continue to rise, their inter-relationships may change. We examined whether caesarean delivery predicts allergic disease and impaired lung function in two contemporary harmonised population-based cohorts.
Methods: Parent-reported asthma and eczema data were drawn from two prospective Australian infant cohorts, HealthNuts (n=5276, born 2006-2010) and the Longitudinal Study of Australian Children (LSAC, n=5107, born 2003-2004) at age 6-7 years, and spirometric lung function from LSAC's Child Health CheckPoint (n=1756) at age 11-12 years. Logistic regression estimated associations between delivery mode and current asthma and eczema at 6-7 years, and linear regression examined lung function at 11-12 years. Models were adjusted for potential confounding factors.
Results: Complete case analysis included 3135 HealthNuts and 3654 LSAC children (32.2% and 30.9% born by caesarean, respectively). An association was evident between caesarean delivery and asthma at age 6-7 years in HealthNuts (adjusted OR (aOR) 1.25, 95% CI 1.00 to 1.57) but not in LSAC (aOR 1.05, 95% CI 0.86 to 1.28), while neither study showed clear associations with eczema (HealthNuts: aOR 1.09, 95% CI 0.88 to 1.35; LSAC: aOR 0.89, 95% CI 0.69 to 1.15). Spirometric lung function parameters at age 11-12 years were similar by delivery mode. Associations were not modified by duration of breast feeding, maternal history of asthma/eczema, childcare attendance, number of older siblings or pet exposure.
Conclusions: In two unselected populations using harmonised protocols, the likely association of caesarean delivery with developing childhood allergy was small.
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