A new analysis of records from India and Vietnam has found a significant association between cesarean birth and childhood asthma. Studies of children born in wealthier countries have produced similar results.
A new analysis of records from India and Vietnam has found a significant association between cesarean birth and childhood asthma. The effect size is similar to those found by studies conducted in rich Western countries and therefore suggests that the underlying mechanism is unrelated either to ethnicity or national income.
Investigators used data from the Young Lives Study to look for ties between cesarean birth and childhood asthma in 2,026 Indian children in 2,000 Vietnamese children. Data concerning delivery method, subsequent respiratory problems and a range of sociodemographic factors came from caregiver questionnaires. Multivariable logistic regression models used propensity score adjustment for a number of known confounders before calculating differing risks for incident asthma.
After accounting for risk factors such as wealth, liveborn parity, low birth weight, geographic location, cooking fuel used, livestock ownership, household size, housing quality and parental smoking, researchers found that Vietnamese children born via cesarean section were twice as likely as vaginally delivered children to develop asthma by age 8 (odds ratio [OR], 2.0; 95% confidence interval [CI], 1.2-3.3). The elevation of asthma risk was even greater for Indian children delivered via cesarean section (OR 2.6; 95% CI, 1.3-5.4).
“The study suggests that cesarean birth may be associated with increased risk of childhood asthma in India and Vietnam,” the study authors wrote in Paediatric and Perinatal Epidemiology. “The underlying mechanisms of this finding need to be further elucidated.”
A number of prior papers have reported similar associations for children in wealthier countries.
A 2005 paper published in Clinical & Experimental Allergy reviewed the medical records of 8,953 children and found that cesarean delivery was associated with a 24% greater risk of subsequent asthma. Further analysis found that the association was gender specific. Boys delivered by cesarean section developed asthma at normal rates, while girls delivered by cesarean section were 53% more likely to develop asthma than vaginally delivered girls. The relationship was even stronger in girls who were delivered via cesarean section after an older sibling had also been delivered via cesarean section (OR, 1.83; 95% CI, 1.13-2.97).
A 2015 review published in the British Medical Journal found 23 different studies linking surgical delivery to elevated childhood asthma rates. The combined data indicate that about 9.5% of surgically delivered babies and about 7.9% of vaginally delivered babies go on to develop asthma.
All of this data, however, comes from the US, Western Europe and other rich countries. The authors of the new study believe they are the first to find that cesarean section is also associated with increased asthma risk in at least 2 middle income countries.
There was no particular reason to think that the association was unique to rich countries. The most common theory for the underlying mechanism is that women pass health-promoting bacteria to their children during vaginally delivery, but this hypothesis is unproven.
“Although there is an increasing body of evidence that the intestinal microbiota play an essential role in the postnatal development of the immune system, the mechanisms remain poorly understood,” the authors of a another review wrote in Clinics in Perinatology. Also, “confounding factors could also play intermediate roles. Data available from several studies indicate a delayed onset of lactation with cesarean section. Thus, many infants born by cesarean delivery also lacked the early support of breast milk as stimulator for a physiological intestinal flora.”