A controversial new meta-study combining higher rates of autism with cesarean birth is criticized by experts for being a perfect example of how correlation is not synonymous with causality. The study estimates that children born by Caesarean section are 33 percent more likely to suffer from autism. However, this statistic is only half the story.
The study was conducted by a team of scientists from Sweden and collected data from 61 studies dealing with more than 20 million babies. The impressive large meta-study concluded that "Cesarean birth is significantly associated with autism spectrum disorder and attention deficit / hyperactivity disorder." Specifically, the study found that cesarean delivery reduces a child's risk of developing autism by 33 percent and the attention deficit increased hyperactivity disorder (ADHD) by 1
It is not the first time that researchers have found a link between autism and cesarean delivery. Previous studies have suggested that one possible explanation for the association could be the stress associated with a C-section in an emergency. In order to evaluate this potential association, the new research separated high-birth rate embryos from elective fasting embryos, but found absolutely no difference in autism risk, suggesting that the association relies solely on the nature of the birth itself.
Are these plans affected by cesarean delivery? 33 percent certainly sounds like a high number.
Andrew Whitehouse, a researcher from the Telethon Kids Institute in Western Australia, says that despite the seemingly high 33 percent statistics, the increased risk identified in the study is actually quite irrelevant.
If the prevalence of these conditions is already relatively low (about 1% for autism and 7% for ADHD), this increase in opportunities is not essential, "Whitehouse explains in an editorial for The Conversation . "In the case of autism, this is a shift in probability from 1% to 1.33%. This shift has no consequences and certainly requires no change in our clinical practice. "
Peter Baghurst of the University of Adelaide points out that one of the commonly known risk factors for autism is premature birth and preterm labor is often associated with caesarean section. Baghurst notes that the meta-study does not seem to take gestational age into account in her calculations.
"Correction for confusion by gestational age can be made in the statistical analysis of cohort studies – even at the design stage (by assigning cases to controls). in case-control studies, "says Baghurst. "While some or all of the 63 studies that contributed to this analysis may have made corrections, this important caveat is not discussed in the main body of this paper, nor is it mentioned if the nature or type of adjustment for the Pregnancy takes place Age was a crucial factor in assessing the quality of each study by the authors who wanted to include it in their meta-analysis. "
Many experts find that a major problem in trying to associate Caesarean section with autism risk is the following: A number of variables leading to caesarean section are also specifically associated with the risk of autism. For example, children of older parents develop autism more often, and older parents are more likely to opt for caesarean delivery. Other similar confounding factors blurring an association between the type of delivery and autism are mothers who suffer from obesity, diabetes, or chronic autoimmune diseases. Without explicit consideration of all these factors, it becomes very difficult to imply a caesarean section, which in itself carries an increased risk of autism in a child's birth and autism, but it is a meaningless association without a strong causal hypothesis.
"Why this relationship exists is unknown, but it is almost certain that Caesarean birth alone does not contribute to a child's chances of developing autism or ADHD," says Whitehouse. "Instead, other pregnancy factors are likely to play a role in this relationship, as well as genetic factors that can interact with the environmental factors during pregnancy to contribute to brain development."
The new study was published in the Journal JAMA Network Open .