Children born by cesarean delivery are at increased risk for developing asthma, particularly if their parents have allergies, according to a report published this month.

C-section has been thought to be a risk factor for asthma, although the relationship is controversial, Dr. H. A. Smit, from the National Institute for Public Health and the Environment in Bilthoven, the Netherlands, and colleagues note in the report.

Smit’s team analyzed data from 2917 children to assess the association between cesarean delivery and asthma or allergies at 8 years of age.

Overall, 362, or 12.4 percent, of the children developed asthma at age 8, the researchers report, and 8.5 percent had been delivered by c-section.

Overall, children delivered by c-section were 79 percent more likely to develop asthma than children born vaginally, the investigators found. The association between c-section and asthma was even stronger for children born to one or two allergic parents than for children born to parents without allergies.

“Our results emphasize the importance of gene-environment interactions on the development of asthma in children,” Smit and colleagues conclude.

“The increased rate of cesarean section is partly due to maternal demand without medical reason. In this situation, the mother should be informed of the risk of asthma for her child, especially when the parents have a history of allergy or asthma,” they wrote.

SOURCE: Thorax, February 2009.