A controversial new metastudy linking higher rates of autism with c-section births is being criticized by experts calling it a perfect example of how correlation does not equal causation. The study suggests children born by cesarean are 33 percent more likely to develop autism, but that statistic is only half of the story.
The research was led by a team of scientists from Sweden, and it gathered data from 61 studies covering over 20 million babies. The impressively large metastudy concluded that, “birth by cesarean delivery was significantly associated with autism spectrum disorder and attention-deficit/hyperactivity disorder.” More specifically, the research found cesarean birth increased a child’s risk of developing autism by 33 percent and attention-deficit hyperactivity disorder (ADHD) by 17 percent.
This is not the first time researchers have found an observational link between autism and cesarean birth. Prior studies have hypothesized a possible reason explaining the link could be the stresses associated with an emergency cesarean. To evaluate this potential association the new research separated emergency cesarean births from elective cesarean births, but absolutely no difference was found in autism risk, leading the study to suggest the association was strictly due to the mode of delivery itself.
So, should those planning cesarean births be concerned? 33 percent surely sounds like a high number.
Andrew Whitehouse, a researcher from the Telethon Kids Institute in Western Australia says the increased risk noted in the study is actually quite inconsequential, despite the seemingly high 33 percent statistic.
“When the prevalence of these conditions is already relatively low (around 1% for autism, and 7% for ADHD), this increase in odds is not substantial,” explains Whitehouse in an editorial for The Conversation. “In the instance of autism, this is a shift in odds from a 1% prevalence to 1.33%. This shift is not consequential and certainly does not call for any change in our clinical practice.”
Peter Baghurst, from the University of Adelaide, points out one of the common known risk factors for autism is preterm birth, and preterm birth is frequently associated with cesarean deliveries. Baghurst notes the metastudy does not seem to account for gestational age in its calculations.
“A correction for confounding by gestational age can be made in the statistical analysis of cohort studies – and at the design stage (by matching cases with controls) in case-control studies,” says Baghurst. “While some or all of the 63 studies contributing to this analysis may have made appropriate corrections, there is no discussion of this important caveat in the main body of this paper – nor is there any mention of whether the nature or type of adjustment for gestational age was a crucial requirement in the authors’ assessment of the quality of the individual studies which they chose to include in their meta-analysis.”
Many experts note that a big problem in trying to link cesarean birth with autism risk is that a number of variables that lead to cesarean deliveries also happen to be specifically associated with autism risk. Children of older parents for example, are more likely to develop autism, and older parents are more likely to electively choose cesarean birth. Other similar confounding factors blurring an association between delivery mode and autism include mothers suffering from obesity, diabetes, or chronic autoimmune diseases.
All these conditions lead to both higher rates of autism and higher chances of cesarean delivery. So without explicitly accounting for all these factors it becomes very difficult to imply cesarean delivery, in and of itself, confers an increased risk of autism in a child.
As Andrew Whitehouse concludes, the metastudy certainly can identify a statistical association between cesarean delivery and autism, but it is a meaningless association without a strong causal hypothesis.
“Why this link exists remains unknown, but it is almost certain that a caesarean delivery alone does not contribute to the odds of a child developing autism or ADHD,” says Whitehouse. “Instead, it is likely that other pregnancy factors play a role in this relationship, as well as genetic factors that may interact with the environmental influences during pregnancy to contribute to brain development.”
The new research was published in the journal JAMA Network Open.
