Pregnant women who take a common epilepsy drug may increase their risk of birth defects, finds a new study.

Women who take topiramate (Topamax) in isolation, or with other epilepsy medications, risk birth defects, a dilemma as epileptics are counselled to take their medications throughout pregnancy to prevent seizures. Seizures have been shown to harm the developing fetus.

Topiramate is also prescribed to prevent migraines.

In the study, conducted by British and Irish researchers, there were 16 major birth defects among 178 live births in patients taking topiramate. Three of these defects were in women taking topiramate on its own and 13 were in those whose mothers were taking it with other epilepsy medications, such as valproate.

The birth defects included four cleft palates or cleft lips, a rate of birth defects 11 times higher than in women not taking the drugs. And four baby boys had genital birth defects, two of them considered major, a rate 14 times higher than in women not on the drugs.

Though the study was small in scope, researchers say the results should be taken into account by physicians when prescribing topiramate.

"These results should also get the attention of women with migraine and their doctors, since topiramate is also used for preventing migraine, which is an even more common condition that also occurs frequently in women of childbearing age," said John Craig, a researcher with the Royal Group of Hospitals in Belfast, Northern Ireland, in a release.

"Clearly these results need to be replicated in larger numbers and from different registers before we might counsel women of child-bearing age against using combinations including topiramate and valproate," reads the study.

The study relied on data regarding topiramate usage before August 2007. It is published in the July 22 issue of Neurology.