Women taking the drugs known as selective serotonin reuptake inhibitors (SSRIs), which are given to treat depression, were almost twice as likely to have a low birth-weight baby as those who were not using the drugs. Almost 20% of the first group gave birth prematurely, while the women without antidepressants had a premature baby rate of 12%.

The women on the drugs were twice as likely to have a stillbirth as the others. The babies of women on SSRIs were also more likely to suffer from seizures.

This is not the first research to suggest that SSRIs may have detrimental effects on babies in the womb. But it is based on firmer evidence about the medication taken by pregnant women, which came from health records between 1990 and 2000 in Saskatchewan, Canada. Previous studies had largely based their findings on personal recollection of pills taken.

Shi Wu Wen and colleagues from the medicine faculty at the University of Ottawa urge more caution in prescribing SSRIs to women who may become pregnant.

Given the doubts, "the risks and benefits of SSRIs for women of reproductive age with severe depression should be considered", they write.

Women should be told about the possible risks of the SSRIs before they are given them and may need to talk to specialists with experience in treating depression rather than GPs, they say.

The study finds a link between the drugs and stillbirths, premature and low birthweight babies, but cannot prove that the antidepressants that the women took were the cause. Tommy's, the UK-based baby charity, said pregnant women should continue taking their medication as normal. It was possible, the charity said, that the damage to the babies arose from the depression itself.

"Left untreated, the physical and psychological effects of depression can lead to problems during pregnancy," said Charlotte Davies, who works for the charity. "Sufferers of depression are far more likely to smoke as well as lose their appetites, and in extreme cases are more likely to attempt suicide, which can all have devastating effects."

The Medicines and Healthcare products Regulatory Agency has warned doctors not to prescribe most SSRI drugs to children, with the exception of Prozac, after evidence of a greater rate of suicidal agitation compared with children taking other treatments for depression.