The association of caesarean section delivery with asthma and atopy in children: Effect modification by family history of allergies

Introduction: Studies on the association of birth by caesarean section and allergies have produced conflicting findings. Evidence on whether this relation may differ in those at risk of atopy is limited. Aim: To investigate the association of mode of delivery with asthma and atopic sensitization and the extend to which this effect is modified by family history of allergies Methods: Asthma outcomes were assessed cross-sectionally in 2216 children aged 8 using the ISAAC questionnaire whilst in a random subgroup of 746 skin prick tests to eleven allergens were also performed. Adjusted odds ratios of asthma and atopy by mode of delivery were estimated in multivariable logistic models. Results: After adjusting for potential confounders, children born by caesarean section as compared to vaginally had significantly higher odds of reporting ever having wheeze (OR 1.36, 95%CI 1.07-1.71), asthma diagnosis (OR 1.41, 95%CI 1.09-1.83) and atopic sensitization (OR 1.67, 95%CI 1.08-2.60). There was some evidence that family history of allergies may modify the effect of caesarean section delivery on atopy (p for effect modification=0.06) but not asthma. More specifically, children with a family history of allergies had double the odds of atopic sensitization if born by caesarean section (OR 2.34, 95%CI 1.20-4.54) whilst a non-significant association was observed in children without a family history of allergies (OR 1.27, 95%CI 0.69-2.36) Conclusion: Birth by caesarean section is associated with asthma and atopic sensitization in childhood. The association of caesarean delivery and atopy but not asthma is more pronounced in children with family history of allergies.