Researchers writing in JAMA Network Open have found a link between birth delivery style and certain neurodevelopmental and psychiatric disorders – but the findings should be taken with a grain of salt, say scientists not involved in the study.
The study's authors came to the conclusion that cesarean births are associated with a small but statistically significant risk of autism and attention deficit hyperactivity disorder, or ADHD, (increasing likelihood by 33 percent and 17 percent respectively) after comparing the results of 61 studies across 19 countries, which combined involved 20 million deliveries since 1999.
But – and it's a big but – this association was not consistent among all studies. What's more, as the authors themselves point out, there may be a third (or confounding) factor that explains both the C-section and the prevalence of the two conditions, which should be explored in future studies.
Of the 29 study populations used to compare autism rates of those born via the vaginal canal and those born via C-section, 17 presented an increased risk that was considered statistically meaningful. The same was true for five of the 14 analyzed for ADHD – as these five were the larger of the 14 studies, the authors say they carried more weight.
Taken together, those studies seem to suggest undergoing C-section raises the child's risk of autism by 33 percent and ADHD by 17 percent. Because the rates of both these conditions are relatively low to start with (1-2 percent for autism and 5 percent, possibly more, for ADHD), the implications are comparatively small.
"Overall, the disorders that were studied were generally uncommon, so that even if increases in risk are really caused by cesarean delivery, the absolute increases in risk are small," Kevin McConway, an emeritus professor of applied statistics at the Open University, UK, who was not involved in the study, said in a statement.
"For ASD, the studies indicate that somewhere around 7 babies in 1,000 had an ASD diagnosis if they had a vaginal delivery, and that that rate might instead be 9 or 10 per 1,000 cesarean deliveries.
"ADHD was a bit more common, with somewhere around 20 or 25 diagnoses per 1,000 vaginal deliveries, which would instead be around 25 or 30 per 1,000 in cesarean deliveries."
But while the results throw up an interesting positive correlation between the two conditions (one that could not be replicated in any of the other disorders looked at, including intellectual disabilities, obsessive-compulsive disorder, and various eating disorders), they do not show a causal effect. Instead, it is more likely that there is a third factor.
Indeed, cesareans are not performed randomly but for medical reasons – and medics are keen to stress that cesareans are safe (sometimes life-saving procedures) provided they're performed by a medically trained professional.
"It is important to note the results do not suggest that cesarean section causes neurodevelopmental disorders. Indeed, there is good evidence from sibling studies that there is no causal link between cesarean section and autism," James Findon, a lecturer in psychology at King's College London who was not involved in the study, said in a statement.
"It is possible that the association stems from a genetic or environmental factor common to both neurodevelopmental disorders and the need for cesarean delivery. Parents should be reassured that cesareans are a largely safe procedure when medically indicated."