Caesarean Babies Linked to Increased Risk of Asthma

Caesarean Babies Linked to Increased Risk of Asthma
2Dec2008 Filed under: Autism Author: Kayla
Babies born by a caesarean delivery appear to have nearly twice the risk of developing asthma by age eight, according to researchers here. Among 2,917 Dutch children followed from birth through age eight, the odds ratio for developing asthma was 1.79 (95% CI 1.27 to 2.51) for those with a cesarean delivery compared with vaginal births, reported Henriette A. Smit, Ph.D., of the National Institute for Public Health and the Environment, and colleagues online in Thorax.

The chance of developing asthma was even greater when, in addition to the cesarean birth, children had two allergic parents (OR 2.91, 95% CI 1.20 to 7.05, versus OR 1.36, 95% CI 0.77 to 2.42, for cesarean birth and no allergic parent).

For cesarean-born children with one allergic parent, the risk of asthma was about the same as in the entire sample (OR 1.86, 95% CI 1.12 to 3.09).

“We conclude that delivery by cesarean is a risk factor for asthma in childhood and that this association is stronger in children with allergic parents,” Dr. Smit and colleagues wrote.

It’s the second large study this year to link cesarean with subsequent development of asthma. A study of 1.7 million Norwegian children, published in June in the Journal of Pediatrics, found a 50% increase in asthma risk associated with those who had a cesarean delivery

In the new Dutch study, the researchers found a cumulative incidence of asthma of 17.1% by age eight among cesarean -born children, compared with 9.8% in those born vaginally.

The researchers also found a strong association between birth method and sensitivity to food and airborne allergens at age eight — but only for children whose parents did not suffer allergies.

The odds ratio for allergic sensitization among caesarean -born children without allergic parents was 2.14 (95% CI 1.16 to 3.98).

For caesarean -born children with one or two allergic parents, however, the odds ratios for sensitization were both less than one (not significant).

Dr. Smit and colleagues said the mechanism underlying the relationship between birth method and asthma and allergy risk is unclear.

However, they said, the “hygiene hypothesis” of asthma development could be factor.

Under this hypothesis, children’s early exposure to allergens and pathogens may dictate their future risk of allergic conditions including asthma.

Dr. Smit and colleagues pointed to an earlier study in which cesarean-born children were affected with postnatal intestinal colonization.

“According to the hygiene hypothesis, this could influence the persistence of the fetal Th2 response during early childhood,” they said.

They added that the lack of association between caesarean -born children and allergic sensitization in children with allergic parents could be an artifact of their study design.

“[It] might be that the level of specific IgE was already high in children with allergic parents because of the strong genetic influence and therefore we did not observe the influence of caesarean section on allergic sensitization,” the researchers postulated.

Dr. Smit and colleagues did not control for race or ethnicity or for socioeconomic status in the study, although they did take account of maternal education and parental occupation.

In the United States, race, ethnicity, and socioeconomic factors are powerful predictors of asthma.

Dr. Smit and colleagues acknowledged that socioeconomic status was a potential confounder.

They also noted that in Holland caesarean sections are uncommon generally and elective procedures are even more so.

In the U.S., caesarean -born children account for close to 30% of births, with elective procedures representing an unknown and possibly substantial proportion.

One study estimated that more than 5% of all live U.S. births in 2001 were caesarean without a medical indication.