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New studies into epilepsy medication and birth defects

22 March, 2005

New studies, reported in the journal Neurology, show mixed results on the effects of anti-epileptic drugs (AEDs) taken during pregnancy.

A study looked at one of the newer AEDs, lamotrigine, and found that the risk of birth defects in children born to women taking the AED during pregnancy was similar to that in women without epilepsy. However, the second study, looking at one of the older AEDs, valproic acid (or sodium valproate) found an increased risk of birth defects.

Research reported in the journal also found that children aged between six and sixteen who had been exposed to valproic acid during pregnancy had lower verbal IQ scores than children exposed to other or non AEDs during pregnancy.

In the lamotrigine study, birth defects in babies whose mothers took the drug during pregnancy were reported over an 11 year period to the International Lamotrigine Pregnancy Registry. Among 414 pregnancies where woman only took lamotrigine in the first three months of their pregnancy there were 12 cases of major birth defects (2.9 per cent). The risk increased to 12.5 per cent for women who were taking lamotrigine along with valproic acid during the first three months.

In an accompanying editorial, neurologist Patricia Penovich, of the Minnesota Epilepsy Group, wrote:

'Even though the number of women enrolled in this study was large, the number of pregnancies is still too small to give us absolute answers. But the results can be somewhat reassuring to women. They also emphasise the importance of trying to control seizures with only one epilepsy drug if possible and the importance of planning carefully how epilepsy drugs will be used during pregnancy before the pregnancy occurs.'

Investigating valproic acid, one study monitored the rate of birth defects in infants whose mothers had taken valproic acid as their only AED during the first three months of pregnancy and were enrolled in the North American Antiepileptic Drug Pregnancy Registry. Of the 149 women in the study, there were 16 infants (10.7 per cent) with birth defects. The women taking valproic acid were nearly three times more likely to have an infant with a birth defect than women taking another AED. They were more than seven times more likely to have an infant with a birth defect than women in the general population.

For the second study on valproic acid, researchers tested 249 children between the ages of six and sixteen born to mothers with epilepsy. The 41 children who were exposed to valproic acid during pregnancy were more likely to have low verbal IQ scores (average of 84) compared to other groups in the study, such as those exposed only to the AED phenytoin (average score of 99) or those not exposed to any AED during pregnancy (average score of 92).

Those exposed to valproic acid were also more likely to have overall IQ scores in the extremely low, or mentally impaired, range. Two to three percent of the population would be expected to fall in this range. In the study, 22 per cent of those exposed to valproic acid were in this range.