0920 Does caesarean section (C/S) predispose to childhood asthma?

It isn’t quite clear why this possible association of asthma and C/S was queried in the first place, but some references imply that the question arose out of observations that asthma was on the increase and frequently in countries in which there was also an increase in C/S rates. Nobody who has researched the issue and found an association has come up with an answer as to causality, and while some say it’s because maternal asthma is likely to be an indication for C/S, most authors invoke the hygiene hypothesis (the lack of exposure to vaginal flora and pathogens, and delayed microbial colonization) or “altered immune responses”. This possible association was highlighted in a full page article in a recent issue of the widely-read Medical Chronicle, citing two papers that reported positive results. However further review of the literature reveals a fairly large number of studies, most of which start out by saying the data are inconclusive and then proceed to either show no association or if they do, throw another confounder into the pot. For example for three large studies that do not show an association there are nine contemporary articles that provide conflicting or confusing data: one cites an association but only in girls; a Seattle study shows it only in children born preterm while another says only in children born at term, and a third says only for asthma occurring before 3 years of age; a twin study shows the asthma increase only in the first twin born by C/S vs vaginally-delivered infants; a Norwegian study finds the asthma rate higher in emergency sections vs elective; a California study says the increase is found regardless of family history while a Dutch study finds that risk increases two-fold if one parent is affected and three-fold if both are affected. Getting back to microbial colonization, a recent paper shows that perinatal probiotic supplementation might decrease IgE-associated allergy at age 5 in infants born by caesaerean section, but to rates below those of vaginally-delivered infants. In other words C/S did not confer a greater risk but probiotics reduced the standard risk by 16%. At this stage one could probably conclude quite safely a) that the jury is still out on the association, and b), that unless there is a coordinated, multi-centre, large scale prospective study a useful meta-analysis of existing data will be almost impossible given the wide range of study designs and research methodologies.

Read more:
Medical Chronicle May 2009: 71
J Pediatr 2008; 153: 112-6
Clin Exp Allergy 2004; 34: 1349-55