PREGNANT women taking the popular antidepressant paroxetine are being urged to consult their doctor after the drug was linked to birth defects.

The Therapeutic Goods Administration, Australia's drug watchdog, said preliminary results in a US study of paroxetine — commonly sold as Aropax — showed one in 25 babies born to mothers on the drug had a birth defect.

Half of the defects were heart problems, but most of these were non-life threatening. The study also found that women who took paroxetine instead of other antidepressants during the first trimester of pregnancy were more likely to have a child with a birth defect.

Birth defects normally occur at a rate of about three in 100, with heart defects in one in every 100 to 200 babies.

Australia's Chief Medical Officer John Horvath said women should not abandon the drug because withdrawal symptoms could be harmful.

"It's important for the small number of women who would be taking this drug not to panic but to review their treatment with their doctor," he said.

A spokeswoman for GlaxoSmithKline, Nikki Capp, said the drug company had written to doctors warning them of the study's findings.

"The main message from the company is paroxetine shouldn't be used in pregnancy, and pregnant women should talk to their doctor," Ms Capp said.

She said the US study, sponsored by GSK, reviewed statistics on birth defects and antidepressant use in early pregnancy, and uncovered the unexpected findings on paroxetine.

The study results are not regarded as conclusive but sent a strong statistical signal of a problem. "It's something that was reported on August 15 to GSK," Ms Capp said. "We told authorities globally the next week and now we are working globally with regulators."

Aropax was launched in Australia in December 1993.

It has received bad publicity in the past year because of links to suicide attempts and withdrawal symptoms, including withdrawal among newborn babies whose mothers used the drug.

More than 200 million prescriptions have been written worldwide since 1993. In Australia in the year to June 2004, more than 1.2 million government-subsidised prescriptions were filled.

Royal Australian College of GPs' Leanne Rowe said all medications were prescribed with caution in pregnant women.

"It is well known antidepressants are category C drugs that are suspected of causing harm in the foetus, although that has been unknown until now because of the lack of study information."

Dr Rowe said the drug produced withdrawal symptoms and any dose should be gradually reduced. "We don't want women to be alarmed and stop the drug abruptly," she said. "We want them to consult their doctor."

The director of beyondblue's postnatal depression program, Anne Buist, said many depressed women were reluctant to take drugs in pregnancy, but up to 10 per cent had severe depression that needed drug treatment.

Associate Professor Buist said ideally women planning children should talk with their doctor and possibly seek alternative psychological treatment. "Suicide is the equal leading cause of maternal death and untreated depression can also have a biological effect on the foetus … these need to be weighed up in each case," she said.

"In many cases, psychological therapies may be the most appropriate ongoing treatment."

Australian Medical Association federal president Mukesh Haikerwal said there had long been questions about prescribing antidepressants to pregnant women, "but it was sometimes the lesser of two evils".

"This study shows the risks can no longer be tolerated for this group of women."