C-section delivery linked to higher risk of childhood asthma.

Nov 30, 2011

Magnus, MC, SE Håberg, H Stigum, P Nafstad, SJ London, S Vangen and W Nystad. 2011. Delivery by cesarean section and early childhood respiratory symptoms and disorders: The Norwegian mother and child cohort study.  American Journal of Epidemiology http://dx.doi.org/10.1093/aje/kwr242.

Synopsis by Renee Gardner

C-section delivery is associated with an increased risk of asthma in young children and may contribute to rising rates of the respiratory disease, finds the largest study to address the question to date.

Children born via cesarean section (C-section) have an increased risk of asthma at age 3, according to the largest study yet on the topic. The risk was higher in children whose mothers did not have asthma when compared to those whose mothers have asthma.

Children whose mothers did not have asthma were a third more likely to have asthma at three years of age if born via C-section. The results suggest that the rising rate of C-section deliveries may be another risk factor contributing to the rising rates of childhood asthma, in addition to known risk factors such as parental smoking and air pollution.

Asthma occurs when airways are inflamed and swollen, leading to the wheezing and shortness of breath that characterize an asthma attack. Any number of allergens and irritants – such as air pollution and tobacco smoke – can trigger an attack. Medications control the symptoms.

Asthma's steady rise in the last decades means it now affects in some way about one in four urban children in the world. While asthma is partly a hereditary disease, experts recognize that environmental factors play a large part in its risk. Especially important may be those present early in life.

Previous studies have largely shown that children born via C-section were more likely to be diagnosed with asthma. The reason is still not clear but researchers believe that children born via C-section may miss exposure to important immune challenges compared to children born via the birth canal. These early immune challenges may teach the immune system how to properly respond to later immune challenges. This may lead to an increased risk of asthma in those children who miss out on these early challenges.

Findings from these prior C-section studies were not always consistent. One problem is many of them did not keep track of other important risk factors for asthma – such as maternal smoking – especially before the asthma was diagnosed.

In the current study, Norwegian researchers examined asthma risk in more than 37,000 children. Information on the method of delivery was obtained from Norwegian medical registries. Mothers entered the study in early pregnancy and completed a questionnaire in which they reported important demographic and lifestyle information. They filled out questionnaires about the children’s health several times after birth and before the children were three years old. They were asked whether the child suffered from wheezing, asthma or recurring respiratory tract infections. Researchers compared the occurrence of these in C-section births with those from natural deliveries.

The researchers were able to account for other important risk factors for asthma, such as smoking and maternal body mass index (BMI). They also accounted for important protective factors for asthma, such as the duration of breast-feeding.

The researchers found that children born via C-section were more likely to have asthma during their first three years. No increased risk of wheezing or recurring infections was found.

Even after accounting for other influences on asthma risk, the children born via C-section were more likely to have asthma, the researchers report in the Journal of Epidemiology. They suggest future studies should examine the relationships with children of different ages.


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