Background: Cesarean section might be a risk factor for asthma due to a delayed microbial colonization, but the association remains controversial.
Objective: To investigate prospectively whether children born by cesarean section are more at risk of having asthma in childhood, and sensitization at the age of 8 years taking into account the parental allergic status.
Methods: We studied 2,917 children, who participated in a birth cohort study and followed for 8 years. The definition of asthma included wheeze, dyspnea and prescription of inhaled steroids. In a subgroup (n=1,454), serum IgE antibodies for inhalant and food allergens were measured at 8 years.
Results: In the total study population, 12.4% (362) of the children had asthma at the age of 8 years. Cesarean section, with a total prevalence of 8.5%, was associated with an increased risk of asthma (odds ratio [OR], 1.79; 95% confidence interval [CI], 1.27-2.51). This association was stronger among predisposed children (with two allergic parents: OR, 2.91; 95% CI, 1.20-7.05; with only one: OR, 1.86; 95% CI, 1.12-3.09) than in children with non-allergic parents (OR, 1.36; 95% CI, 0.77-2.42). The association between cesarean section and sensitization at the age of 8 years was significant only in children of non-allergic parents (OR, 2.14; 95% CI, 1.16-3.98).
Conclusions: Children born by cesarean section have a higher risk of asthma than those born by vaginal delivery, particularly children of allergic parents. Cesarean section increases the risk for sensitization to common allergens, in children with non-allergic parents only.