WEDNESDAY, Jan. 23 (HealthDay News) -- Children of mothers who take the antiepileptic drug valproate during pregnancy have lower IQ scores at age 6, a new study says.

And the higher the dose of valproate during pregnancy, the greater the effect on a child's IQ, according to the report published in the Jan. 22 issue of The Lancet Neurology.

For the study, the researchers looked at 305 pregnant women in the United States and United Kingdom who took a single drug to treat the seizure disorder -- either valproate (Depakote), carbamazepine (Tegretol), lamotrigine (Lamictal) or phenytoin (Dilantin).

At age 6, the IQ of children whose mothers took valproate during pregnancy was seven to 10 points lower than children whose mothers took another antiepileptic drug. Exposure to valproate was also associated with poorer speaking and memory abilities.

"These results build on our earlier work to show that valproate usage during pregnancy has a significant negative effect on children's IQ, which lasts beyond their earliest years," said study leader Kimford Meador, a professor in the neurology department at Emory University in Atlanta.

"IQ at age 6 is strongly predictive of adult IQ and school performance, so our research suggests that valproate use during pregnancy is likely to have long-term negative effects on a child's IQ and other cognitive [mental] abilities," Meador added in a journal news release.

Another expert said the study is practice-changing.

"This important work has changed the way we practice neurology, leading us to conclude that valproate should not be used, if at all possible, in women of child-bearing potential," said Dr. Cynthia Harden, chief of the division of epilepsy and electroencephalography at the Cushing Neuroscience Institute in Manhasset, N.Y.

"The risks of valproate during pregnancy are clearly demonstrated, as the children in this research cohort continue to grow," said Harden.

However, the researchers also found that over time IQ may improve for children exposed to valproate in the womb, and that folic acid supplementation in mothers-to-be may improve children's IQ scores.

Harden called the finding about folic acid's mitigating effect "reassuring and fascinating, since the mechanism of how intrauterine valproate exposure causes cognitive [thinking] and behavioral problems in children is unknown."

For some patients, valproate is the only drug that can control their seizures. This may give particular importance to the findings that higher drug doses have a greater impact on IQ and that folic acid supplementation may have a positive effect on IQ, the researchers said.

Meador said more research in this area is urgently needed, given that many women with epilepsy do not have the option of stopping medication during pregnancy.

After a 2009 study found that taking valproate during pregnancy affected children's IQ at age 3, the U.S. Food and Drug Administration issued a warning that valproate exposure in the womb is associated with impaired mental function in children.

More information

The Epilepsy Foundation has more about pregnancy and epilepsy medications.