Children exposed to antidepressants during pregnancy seem to be at a slightly higher risk of autism than children of mothers with psychiatric disorders who were not treated with antidepressants during pregnancy, according to a University of Bristol study published in The BMJ today. However, the researchers stress that the absolute risk of autism was small, so these results should not be considered alarming.

Several studies have reported associations between antidepressant use during pregnancy and autism in offspring. But it is not clear whether this is due to the underlying illness, antidepressant drugs, or other unmeasured factors.

In a bid to better understand the reasons behind this association - a research team led by Dr Dheeraj Rai at the University of Bristol’s Population Health Science Institute, applied a range of analytical methods to a large Swedish population.

They analysed data from 254,610 individuals aged 4-17, including 5,378 with autism, living in Stockholm in 2001-11 who were born to mothers who did not take antidepressants and did not have any psychiatric disorder, mothers who took antidepressants during pregnancy, or mothers with psychiatric disorders who did not take antidepressants during pregnancy.

Of the 3,342 children exposed to antidepressants during pregnancy, 4.1 per cent (136) had a diagnosis of autism compared with 2.9 per cent (353) in 12,325 children not exposed to antidepressants whose mothers had a history of a psychiatric disorder.

There was no evidence of any increased risk of autism in children whose fathers were prescribed antidepressants during the mothers’ pregnancy.

The results of the various analyses seemed to be consistent with each other, say the authors, suggesting that the association between antidepressant use in pregnancy and autism might not be fully explained by other factors. They point to some study limitations, such as lack of detailed measures of severity of depression. However key strengths were the large sample size and the range of analyses carried out to minimise bias.

It is important to note that the absolute risk was small (over 95 per cent of women in the study who took antidepressants during pregnancy did not have a child with autism), stress the authors.

They estimate that, even if the association between antidepressant use and autism is causal, only 2 per cent of cases would be prevented if no women with psychiatric disorders used antidepressants during pregnancy.

They call for “a balanced discussion in relation to clinical decision making in the light of evolving but yet inconsistent evidence” and say “it is important to continue investigation of possible underlying biological mechanisms that could help us to better understand the aetiology of autism.”

Commenting on how families and doctors making decisions about antidepressants during pregnancy should interpret the results, Dr Rai said: "Our advice for pregnant women and clinicians is very clear. They should not base decisions about the use of antidepressants during pregnancy on any one study, especially when the research evidence is conflicting, as in this case where different studies have reached different conclusions.

"There could be severe risks of stopping or not taking antidepressants during pregnancy both to the mother and the foetus so the benefits of these medications for mothers who need them should not be forgotten.

"Balancing benefits and risks of taking medications during pregnancy is a complex and often difficult decision and our advice would be for women to discuss their concerns with their treating clinicians who will be able to help them weigh the pros and cons."