A study involving 655,615 children born between 1996 and 2006 found that 4.42 per cent of those whose mothers used the drug valproate while pregnant were diagnosed with an autism- spectrum disorder, which can range from mild to more severe forms. The research also found that 2.5 per cent were found to have childhood autism.
Researchers called for more studies to back up their findings, saying drugs to treat epilepsy were important for controlling the condition in pregnancy.
It is estimated that about one in 100 people in the UK is affected by an autism-spectrum disorder.
The study, published in the Journal of the American Medical Association, focused on valproate, which is used to treat epilepsy and other neuro-psychological disorders.
The study says: “Anti-epileptic drug exposure during pregnancy has been associated with an increased risk for congenital malformations and delayed cognitive development in the offspring, but little is known about the risk of other serious neuropsychiatric disorders.”
Jakob Christensen and colleagues from Aarhus University Hospital in Denmark assessed the link between use of the drug during pregnancy and the risk of autism in the babies born.
The study included all children born in Denmark from 1996 to 2006, with national registers used to identify children exposed to valproate during pregnancy and diagnosed with autism-spectrum disorders, including Asperger’s syndrome.
During the study period, 5,437 children were diagnosed with autism-spectrum disorder, including 2,067 with childhood autism. The researchers identified 2,644 children exposed to anti-epileptic drugs during pregnancy, including 508 exposed to valproate.
They found that use of valproate during pregnancy was associated with an absolute risk of 4.42 per cent for autism-spectrum disorder – the equivalent of one in 20 – and an absolute risk of 2.5 per cent for childhood autism – about one in 40. The study found that for the rest of the children, 1.5 per cent had an autism-spectrum disorder.
The researchers said: “Because autism-spectrum disorders are serious conditions with lifelong implications for affected children and their families, even a moderate increase in risk may have major health importance.
“Still, the absolute risk of autism-spectrum disorder was less than 5 per cent, which is important to take into account when counselling women about the use of valproate in pregnancy.”
The authors warned that the findings had to be balanced against the benefits of valproate for epilepsy control.
Dr Robert Moffat, national director of the National Autistic Society Scotland, said: “The causes of autism are complex and are still being investigated. We therefore urge people not to jump to conclusions about this study and its implications.
“It’s important that anyone who does have concerns about their medication seeks advice from an appropriate medical professional.”