Researchers have found women using antipressant drugs in the later stages of pregnancy had autism diagnosed in children under seven years of age.

London -

Taking antidepressants during pregnancy could almost double the risk of a child being diagnosed with autism in the first years of life, a major study of nearly 150 000 pregnancies has suggested.

Researchers have found a link between women in the later stages of pregnancy who were prescribed one of the most common types of antidepressant drugs, and autism diagnosed in children under seven years of age.

A survey of medical records in the Canadian province of Québec found women given selective serotonin reuptake inhibitors (SSRIs), such as Prozac and Zoloft, between the fourth and ninth month of pregnancy were 87 percent more likely to have a child with autism compared with mothers not on antidepressants.

Although the association was statistically significant, the study was not able to prove that the drugs taken during pregnancy were the cause of the children's autism. However, the researchers tried to eliminate other possible reasons such as genetics, maternal age and poverty.

Other experts warned that the findings were still preliminary and could cause alarm given that up to one in 10 pregnant women suffer depression and many are prescribed because they have fewer side-effects.

Scientists not involved in the study said there might be other compounding factors and urged pregnant women prescribed antidepressants not to stop their medication.

“It is possible that the higher risk of autism spectrum disorder is due to the medication, but it may also be due to the effects of the mood disorder for which the medication has been prescribed,” said Professor Ian Jones, director of the National Centre for Mental Health at Cardiff University.

“There may be risks with taking antidepressants, but there are also significant risks from not receiving treatment.”

Seena Fazel, Professor of forensic psychiatry at Oxford University, added: “The problem with this study is that the authors don't have the necessary information on potentially important background factors, which in this case will be genetic risks for autism.”

The study, published in the Journal of the American Medical Association Pediatrics, reviewed the medical records of 145 456 children born in Québec between 1998 and 2009, and their mothers.

The scientists investigated a wide range of factors other than antidepressants that might have influenced the findings but concluded that SSRIs were the strongest link.

“The variety of causes of autism remain unclear, but studies have shown that both genetics and environment can play a role,” Professor Bérard said. “Our study has established that taking antidepressants during the second or third trimester of pregnancy almost doubles the risk that the child will be diagnosed with autism by age seven.”

About 4 732 infants, or 3.2 percent of the children in the study, had been exposed in the womb to antidepressants, most during the first three months of pregnancy. However, the study found that the 2 532 children exposed to the drugs in the second or third trimester were at 87 percent increased risk of autism.

The absolute numbers were small: only 32 infants exposed to antidepressants during the second or third trimester were diagnosed with autism - 1.2 percent of the total number of infants exposed in the womb. This compared with an overall autism rate of 0.72 percent.

The Independent