A controversial meta-analysis claiming to show an increased risk of autism and ADHD among children delivered by caesarean section has been criticised as too broad to yield a meaningful result.
Led by doctoral student Tianyang Zhang from the Karolinksa Institute in Sweden and published in JAMA Network Open, yesterday the review analysed more than 60 studied involving 20 million births, dating back to the 1960s.
It found that C-sections, whether elective or emergency, increased the baby’s odds of autism spectrum disorder by 33% and ADHD by 17%. Being a systematic review, it could not control for any of the numerous variables that could link delivery and neurodevelopmental outcomes such as maternal age, gestational age, indication for caesarean and so on.
Dr Gino Pecoraro, associate professor of obstetrics and gynaecology at the University of Queensland and a federal councillor for the National Association of Specialist Obstetricians and Gynaecologists, said the paper showed the limitations of systematic reviews: the large number did not mean like was being compared with like.
“It really just is a meta-analysis looking at many, many studies that were never designed to look at this question, and it really is data-dredging,” he told The Medical Republic.
“Even though it looked at 20 million people, they were disparate in time – practices that were acceptable in the 1960s would not be accepted now, definitions and diagnostic criteria have changed, and a heap of other things have happened that are not allowed for in this study.
“We know caesarean rates have increased for many reasons including maternal age, obesity and educated women with more options who can choose to have a caesar. We also know that advancing age of the father is independently associated with having children who have ADHD and autism.
“The author’s right to say at the end that this just shows further research is required. There’s nothing in this meta-analysis that would make me change my obstetric practice.”
Dr Pecoraro was preparing for a welter of media hype following the study’s publication, and said there had been a trend in rich countries of vilifying medical intervention in childbirth.
“I think it’s good to have an inquiring mind and look for associations – not causations – because it may well be that the people who have caesareans have some totally unrelated factor that may increase the risk [of neurodevelopmental conditions]. So I welcome people doing the research, but you have to be careful how you interpret things and we mustn’t undo the good that’s been done with having babies.
“Australia’s now one of the safest countries in the world to have a baby. Sure, caesarean rates have increased for many reasons. But it would be a failure of the scientific process if someone read this and interpreted it in a way that denied a person having a caesarean who needed one.
“It won’t be changing my practice.”
Dr Alex Polyakov, clinical director of Melbourne IVF at the Royal Women’s Hospital, noted the vast differences among the studies reviewed. In the most disparate studies, the prevalences of autism and ADHD varied by an order of magnitude, making it impossible to judge the clinical importance of any increase in risk.
“One must question the wisdom of combining such divergent studies and expecting an accurate and unbiased estimation of risk,” he said. “The old saying from computer science, ‘garbage in, garbage out’, seems to apply, as poor quality input will invariably produce sub-optimal output.
“The study adds another possible risk to indiscriminate utilisation of caesarean section as the preferred mode of delivery, but it must be balanced against recognised risks of alternative delivery strategies.”