Experts Debunk Study Highlighting Link Between C-Sections And Autism
Australian health experts have dubbed an international study suggesting there's a link between caesarean births and autism as "flawed" and "unreliable."
The review of dozens of studies and over 20 million births found children who are born by c-section are 33 percent more likely to develop autism over those born by vaginal delivery.
The controversial findings released Wednesday by researchers at the Karolinska Institute in Sweden, also highlighted a 17 percent increased risk of attention-deficit hyperactivity disorder (ADHD).
These associations were similar for children born by either elective or emergency caesarean section.
But multiple health experts have raised concerns about the findings, saying an association between caesarean births and neurodevelopment conditions such as autism does not imply a direct cause. They also don't want expectant mothers to avoid c-sections based on the Swedish findings.
According to the researchers, global caesarean rates have risen from approximately six percent in 1990 to 21 percent in 2015.
Over a similar time period, there has been an increase in the diagnosis of neurodevelopmental disorders, particularly autism.
While the association between them has been known for decades, the researchers of this study combined data from 67 studies -- conducted across 19 countries, including Australia -- to "quantify the extent of the association".
The studies were chosen based on researchers' inclusion criteria.
Analysis of 27 studies that reported on the association between caesarean delivery and autism spectrum disorder (ASD) found the increased odds -- 33 percent --was large enough to be statistically important.
Other disorders, such as learning disabilities and tic disorders, had similar odds but were less "statistically significant", given the modest number of studies.
Associate Professor Jason Howitt, Research Director for the School of Health Sciences at Swinburne University, said the modest increase in autism odds was unsubstantial, given the prevalence of the disorder.
"I believe that the findings are significantly flawed given that a number of the studies used for the analysis had incredibly high rates of autism (between 10-70 percent)," Howitt said.
"This indicates that the data is heavily biased and not consistent with worldwide rates of autism of between one and three percent of all births."
Other experts were concerned by the "heterogeneous" nature of the paper -- a limitation also acknowledged by researchers -- that rendered the findings unreliable.
"The studies analysed were very different and all were observational studies that do not allow for a wide variety of potential biases," Emeritus Professor Alastair MacLeennan AO, Head of the Australian Collaborative Cerebral Palsy Group said.
"Although an interesting and controversial topic the many methodological weaknesses of this study make any conclusion very unreliable."
He said there was a lack of adjustment of "cofounders", such as age -- a limitation also acknowledged by researchers.
Professor Jeffrey Keelan, Deputy Director of the Women and Infants Research Foundation at the University of Western Australia, agreed.
"Due to the nature of the study, the researchers were unable to adequately adjust for the many factors which could link mode of delivery with neurodevelopmental outcomes," he said, citing the mother's age, indication for C-section, the sex of the offspring and underlying or genetic risk factors.
To put it bluntly, Dr Alex Polyakov, an obstetrician, gynaecologist and University of Melbourne lecturer, applied the term, 'garbage in, garbage out'.
"One must question the wisdom of such divergent studies and expecting an accurate and unbiased estimation of risk. The old saying from computer science -- 'garbage in, garbage out' -- seems to apply, as poor quality input will invariably product sub-optimal output.
Correlation Does Not Equal A Cause
The Swedish researchers acknowledged the mechanisms underlying their findings remains unknown, and that more work is needed to examine whether c-sections play a causal role.
This was a soft spot for many experts.
While Keelan said the study is "interesting and well-performed" he said the big question remains: "what is the causal connection, if any, underpinning these findings?"
Most experts who have responded to the study agreed that further information is needed to evaluate the researchers' work.
"Even if the final results are accepted, it is almost possible to assess their clinical significance," Polyakov said.
According to MacLennan, genetic causes are now being confirmed for many of these neurodevelopment disorders and are "unaffected by obstetric management".
Importantly, Howitt said the findings should not alter any parent's decision on the type of delivery for their child.
"Nor should any mother who has an autistic child think that their birth choice could have caused autism -- this is simply not true," he said.
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