A disturbing number of pregnant women are still taking medications that are known to be dangerous to their unborn babies, new research reveals.

The study, led by researchers at Universite de Montreal, found that more than six per cent of pregnant Quebecers in the study took prescription medications that are known to increase the risk for birth defects.

Half these women chose to have abortions to terminate their pregnancy.

The authors conclude that between 800 and 2,000 babies are born every year in Quebec with birth defects that could have been avoided if the mothers had not taken dangerous medications. And many of those birth defects will lead to the premature death of the child.

The study, led by Anick Bérard, a professor at the Université de Montréal's Faculty of Pharmacy, examined data on 109,344 Quebec women who became pregnant between 1998 and 2002.

Using data from the Quebec Pregnancy Registry, the research team found that 6,871 of the pregnant women filled out at least one prescription for one of 11 prescription drugs that are known to be harmful to fetuses, such as anti-seizure medications, psychiatric medications and anticoagulation medications.

Of those women, 3,229 chose to have an abortion. Another six per cent had a miscarriage, while 8.2 per cent gave birth to a child with major birth defects.

"I never expected such results and I was extremely surprised," Bérard, the director of the Research Unit on Medications and Pregnancy of the Sainte-Justine University Hospital Center, said in a statement.

The study will be published in an upcoming issue of the British Journal of Obstetrics and Gynaecology.

While the risk of having a child with a birth defect for any woman is about three per cent, some medications raise that risk ten-fold.

That means that about one in three babies born to women on those medications will have a birth defect, such as malformed limbs or a hole in the heart.

Many of these women, upon learning of the risks, choose an abortion. For example, of the 73 pregnant women in the study who used isotretinoin, a medication used to treat moderate to severe acne and that carries a birth defect risk of about 30 per cent, 57 terminated the pregnancy.

Bérard was shocked to discover how many medications are still available on the market in Canada without proper risk management programs. Such programs often include regular pregnancy testing for all reproductive-aged females and dispensing restrictions to limit women to a 30-day supply.

Berard also believes many potentially dangerous drugs are overused, like benzodiazepines such as Xanax, which are used to treat anxiety.

But other medications cannot be avoided, such as anti-seizure medications for women with epilepsy.

"In those cases, the pregnancy must be carefully planned and medication use must be at a strict minimum during the first trimester," she stressed. "And the expectant mother must meet with her physician regularly."