Caesarean births have been increasing all over the world – particularly elective caesareans. Around the world, the rate of caesareans increased from about six per cent in 1990 to 21 per cent in 2015, a three-fold increase.
That’s been of concern to public health researchers because caesarean deliveries have been controversially linked to negative health outcomes, including obesity, asthma, allergy and diabetes. Less, however, is known about the connections between caesareans and developmental disorders such as autism and ADHD.
In this systematic review – which collected information on more than 60 high-quality studies – the researchers set out to determine the links, if any, between caesarean delivery, neurodevelopmental and psychiatric disorders.
The studies they collected looked at more than 20 million births over multiple countries, providing a rich data pool to analyse. The conditions they were looking for included autism, ADHD, intellectual disability, obsessive compulsive disorder (OCD) and depression.
By splitting the births into two groups – vaginal delivery and caesarean delivery – they could see if there were differences between those groups in how often certain conditions occurred. Since the sample size was so huge – about 20 million births – it made it less likely the results were due to chance or statistical error.
The researchers found that a caesarean delivery increased the risk of autism by 33 per cent, relative to babies born vaginally.
Further, there was a 17 per cent increased risk of ADHD. While these numbers may sound large, it’s important to put them into context. They’re relative differences between two groups, and the absolute increase in risk is much smaller.
There could be some relationship but the risk is small – if it’s there at all.
Given there’s about a one per cent chance of a baby being born with autism, an increase of 33 per cent on top of that only increases the overall risk to 1.3 per cent – which many doctors wouldn’t consider clinically significant.
While headlines can cause alarm in the way they talk about cause, effect and risk, it’s important to put those numbers into context.
There may be some relationship between autism and caesarean delivery, but the nature of that link remains unclear, and it’ll take more investigation to work out what’s going on. In the meantime, the difference in overall risk – if indeed, an increase in risk does exist at all – is so small as to be insignificant.