Folic acid antagonist drugs - often used for treating epilepsy, mood disorders and urinary tract infections - can affect a healthy pregnancy and birth. Expectant mothers who take the drugs are much more likely to suffer a still birth or give birth to a baby that is underdeveloped.
A new study has discovered that the drugs are especially dangerous if taken by pregnant women during the first or second trimester.
It's already known that the drugs can cause neural tube defects, heart problems, oral clefts and urinary tract defects, but it wasn't clear to what extent they can affect the placenta.
The new study, carried out by researchers from the University of Ottawa, analysed the outcomes of 14,982 women who had taken folic acid antagonists, and who were compared to more than 59,000 women who hadn't taken the drugs.
Women who took the drug were nearly twice as likely to suffer pre-eclampsia, and were also more likely to have a baby that was under-developed, or was still born.
(Source: Canadian Medical Association Journal, December 2, 2008; 179 (12). Doi: 10.1503/cmaj.080859).