NEW YORK (Reuters Health) – Among children with a parental history of allergies or asthma, having been delivered by cesarean section appears to increases the odds that they will develop allergic rhinitis and atopy — but not asthma — US researchers report.

“To our knowledge, this is the first prospective birth cohort study of the relation between birth by cesarean section and atopy and allergic diseases at school age among children at high risk for atopy,” Dr. Juan C. Celedon, from Harvard Medical School in Boston, and colleagues note in the Journal of Allergy and Clinical Immunology for August.

The study involved 432 children who were followed from birth to 9 years of age. One or both parents had a history of allergies or asthma. Physician-diagnosed asthma and allergic rhinitis in the children were assessed via caregiver interviews conducted at least twice a year. Allergy skin testing was performed in 271 children at an average age of 7.4 years.

Children born by cesarean section were 2.1-times more likely to develop atopy than their peers born by vaginal delivery, the report indicates.

Similarly, the authors found that cesarean section increased the risk of allergic rhinitis 1.8-fold. As noted, however, c-section did not increase the risk of asthma, or wheeze.

Considering that other studies have identified c-section as risk factor for asthma, the authors believe that the null finding in their study may simply be due to limited statistical power to detect an association. However, they point out that their study was adequately powered to look for an association with wheeze, a major asthma symptom.

Dr. Celedon and colleagues speculate that the lack of exposure to maternal vaginal/fecal flora during c-section and the absence of labor could both have indirect immunologic effects that promote atopy.

Reference:
J Allergy Clin Immunol 2008;122:274-279.