The analysis, published in JAMA Network Open, looked at previous studies including data from more than 20 million births, finding that there was a marginally increased risk of a child developing autismo ou TDAH if they were delivered through cesariana. The findings combined 61 studies from 19 countries dating back to 1999. However, the study did not suggest that caesarean deliveries cause autism or ADHD, only that there was an association.

The association found was very small. Children delivered by caesarean section were 1.33 times more likely to develop autism and 1.17 times more likely to develop ADHD. The risk of being diagnosed with autism or ADHD is already low, at around 1% and 7% for autism and ADHD respectively. This means that the risk of a child developing autism increases to around 1.33% if they are born via caesarean section rather than vaginally.

Both ADHD and autism are developmental disorders. Autistic spectrum conditions affect how someone communicates with and relates to other people. ADHD affects behaviour including concentration, hyperactivity and difficulty staying focused

The results and reporting of this meta-analysis are being contested by experts as an association between caesarean sections and developmental disorders does not mean that delivery by caesarean section causes ADHD and autism.

There are many factors which increase the chances of someone choosing or needing a caesarean section rather than a vaginal birth. Women who are obesas and older, as well as those who have a history of immune conditions like asma, are more likely to have a caesarean section, says Andrew Whitehouse, Professor of Autism Research at the Telethon Kids Institute and the University of Western Australia.

"All of these factors have also been linked with an increased chance of having a child with autism, and it is entirely possible - and some would argue, probable - that it is more likely these factors underlie the relationship between caesarean section and neurodevelopmental disorders," he said in an article for The Conversation.

The researchers have said that more research is necessary in order to find the factors behind the association between caesarean sections and developmental disorders.

"This systematic review and meta-analysis shows an association between caesarean birth and autism and ADHD, but a number of underlying factors which may have led to the development of these conditions were not accounted for. Therefore, the findings of this paper do not show that caesarean birth leads to autism and ADHD," said Dr Pat O'Brien, Consultant Obstetrician and Spokesperson for the Royal College of Obstetricians and Gynaecologists.

"Women who have a caesarean birth should be reassured that it is a safe procedure. In many cases, a caesarean birth can be a lifesaving intervention, as well as the right choice for mother and baby. The vast majority of caesareans in the UK are performed for medical reasons, and should a woman request a caesarean, this should be fully supported in line with guidance from The National Institute for Health and Care Excellence."

Este estudo foi publicado em JAMA Network Open.