Toddlers born to women who took the epilepsy drug valproate while pregnant had lower IQs than children of women who used other similar medications, new research finds.
The study authors say the findings are yet more evidence that the drug should not be given to women who could become pregnant.
"This finding supports a recommendation that valproate not be used as a first-choice drug in women of childbearing potential," Kimford Meador of Emory University in Atlanta and colleagues wrote in the New England Journal of Medicine.
Valproate is designed to reduce seizures in those with epilepsy. But Meador says most prescriptions are written for those suffering migraine headaches, bipolar disorder or other mood disorders.
The drug has been linked in previous research to birth defects, particularly spina bifida. British researchers found in December that it appeared to raise the risk of autism.
Women of childbearing age have long been advised to avoid valproate, which is sold in Canada under such names as Depakote, Depakene and Depacon. Yet it is still widely prescribed by family doctors who have not heard of its dangers, Meador says.
For this latest study, researchers followed pregnant women in the United States and United Kingdom between 1999 and 2004 who were taking one of four anti-epilepsy medications.
They then assessed the cognitive function of the resulting children when they reached three years of age. They found that the children of moms who took valproate had IQ scores six to nine points lower than those who took the other medications.
Toddlers whose mothers had taken valproate had IQs of 92, on average. In contrast, IQ scores were in the range of 98 to 101 for children of women who had taken lamotrigine, phenytoin and carbamazepine. A child of average intelligence should score 100.
The higher the dosage of valproate a woman had taken, the lower the IQ of the child, the researchers found. For the other drugs, dosage levels made no significant difference.
While the number of children in the study is small, which increases the likelihood that other factors influenced the results, the study is the largest to date to show a connection between valproate and diminished IQ.
In the United States, about 25,000 children are born each year to women who have epilepsy, a brain disorder that causes people to have recurring seizures.
Women on the drug who want to get pregnant should plan their pregnancies carefully and consult with a doctor, wrote Swedish researcher Dr. Torbjorn Tomson, in an editorial that accompanied the new study.
Switching drugs after a woman realizes she is pregnant is unlikely to reduce the risk of birth defects. And abruptly stopping the medication may endanger the mother and the fetus, he wrote.
Meador's study is ongoing and the researchers plan to evaluate the children again in another three years.
