“Delivery by CS [Caesarean section] is associated with a modest increased odds of ASD [autism spectrum disorder], and possibly ADHD [attention deficit hyperactivity disorder], when compared to vaginal delivery”.
That was the conclusion reached by the systematic review and meta-analysis completed by Eileen Curran and colleagues* from University College Cork, Ireland. The reported increased risk of ASD following Caesarean section – estimated at 23% – was based on an analysis of some 1.2 million study participants including nearly 13,000 people with a diagnosis of autism or ASD. Further analysis conducted by the researchers based on the concept of population attributable fraction, defined by the World Health Organization (WHO) as “the proportional reduction in population disease or mortality that would occur if exposure to a risk factor were reduced to an alternative ideal exposure scenario”, suggested that some 5% of cases of autism “may be attributable to delivery by CS assuming the observed association is causal”.
As startling as such data might seem, the authors have stressed the need for caution in interpreting their findings. Delivery by Caesarean section is not an uncommon occurrence in modern times and not every child born by this method goes on to develop autism. Similarly, Caesarean section delivery is not a universal factor behind every case of autism.
Such findings cannot however simply be ignored in light of the study methods undertaken by Curran and colleagues based on a pooling of existing peer-reviewed research data, representing the gold-standard of the scientific method. That the authors discuss the possible association between their findings and a growing body of research looking at the collected gut bacteria which inhabit the human body at the point of entry into the world is also an interesting point. Other studies have suggested that vaginal delivery, whereby a baby traverses the birth canal and along the way picks up mother’s bacteria which is then programmed into the developing immune system, might confer some protection against various conditions in child- and adulthood may well be pertinent to discussions on Caesarean section delivery and any increased autism risk. Bypassing the important early exposure to certain types of bacteria carried by the mother inferred by the use of elective Caesarean section offers some potentially testable hypotheses linking gut bacteria and behaviour and development.
* Curran EA. et al. Research Review: Birth by Caesarean section and development of autism spectrum disorder and attention-deficit/hyperactivity disorder: a systematic review and meta-analysis. Journal of Child Psychology and Psychiatry. 2014. October 27.