Serum folate concentrations during pregnancy in women with epilepsy.

Serum folate concentrations, blood counts, and antiepileptic drug concentrations were measured during 133 pregnancies of 125 women with epilepsy. There was an inverse correlation between serum folate concentrations and concentrations of phenytoin and phenobarbitone. The number of epileptic seizures during pregnancy showed no association with serum folate concentrations. No cases of maternal tissue folate deficiency or fetal damage attributable to low maternal serum folate were observed. Maternal serum folate concentrations for infants with structural birth defects, "fetal hydantoin syndrome," or perinatal death were similar to those for healthy babies. A low dose (100 to 1000 micrograms daily) of folate supplement appeared sufficient for pregnant women with epilepsy despite the antifolic action of antiepileptic medication. Monitoring folate concentrations in pregnant women with high serum concentrations of phenytoin or phenobarbitone is recommended.