Birth by cesarean section, allergic rhinitis, and allergic sensitization among children with a parental history of atopy

Background: Cesarean delivery can alter neonatal immune responses and increase the risk of atopy. Studies of the relation between cesarean delivery and allergic diseases in children not selected on the basis of a family history of atopy have yielded inconsistent findings. Objective: We sought to examine the relation between birth by cesarean delivery and atopy and allergic diseases in children at risk for atopy. Methods: We examined the relation between mode of delivery and the development of atopy and allergic diseases among 432 children with a parental history of atopy followed from birth to age 9 years. Asthma was defined as physician-diagnosed. asthma and wheeze in the previous year, and allergic rhinitis was defined as physician-diagnosed allergic rhinitis and naso-ocular symptoms apart from colds in the previous year. Atopy was considered present at school,age if there was 1 or more positive skin test response or specific IgE to common allergens. Stepwise logistic regression was used to study the relation between cesarean delivery and the outcomes of interest. Results: After adjustment for other covariates, children born by cesarean section had 2-fold higher odds of atopy than those born by vaginal delivery (odds ratio, 2.1; 95% CI, 1.1-3.9). In multivariate analyses birth by cesarean section was significantly associated with increased odds of allergic rhinitis (odds ratio, 1.8; 95% CI, 1.0-3.1) but not with asthma. Conclusions: Our findings suggest that cesarean delivery is associated with allergic rhinitis and atopy among children with a parental history of asthma or allergies. This could be explained by lack of contact with the maternal vaginal/fecal flora or reduced/absent labor during cesarean delivery.