NEW YORK (Reuters Health) - Among children who have a parent with allergies or asthma, delivery cesarean section appears to increase the odds that they will develop allergic rhinitis and atopy -- but not asthma -- US researchers report.

The investigators note that to the best of our knowledge, this is the first study to look at the "relationship 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.

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 was assessed using 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, cesarean section did not increase the risk of asthma or wheeze.

Allergic rhinitis, sometimes called "hay fever", refers to a group of symptoms that mimic a common cold such as nasal congestion, sneezing, itching and tearing eyes. Atopy is the innate tendency to develop the classic allergic diseases, such as allergic rhinitis and asthma. It involves the overstimulation of the immune system in response to common environmental proteins such as house dust mite, grass pollen, and food allergens.

Considering that other studies have identified cesarean section as a risk factor for asthma, the authors believe that the lack of association between cesarean section and asthma may simply be due to limited statistical power of the study to detect it. However, they point out that their study was adequately powered to look for an association with wheeze, a major asthma symptom.

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

SOURCE: Journal of Allergy and Clinical Immunology, August 2, 2008.

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