The vitamin folic acid (also known as folate) is important in the production of blood cells and may be important for some nerves. The babies of women who don't get enough of it in the early stages of pregnancy are more likely to have birth defects, especially a type called neural tube defects, which affect the brain and spinal cord. The best known of these is spina bifida, in which the spinal column is not completely closed. By the time a woman knows for sure that she is pregnant, it is probably too late to prevent these defects, so the safest course is for young women to take enough folic acid all the time.

For this reason, all teenage girls and women who could possibly become pregnant are advised to consume at least 400 micrograms (mcg)—equivalent to 0.4 milligrams (mg)—of folic acid per day in either food or a supplement. Most multivitamin tablets or a serving of some fortified cereals will provide this recommended amount. In the United States, the government has required all bread, flour, and similar products to be fortified with folic acid since the 1990s. Folic acid is also found in leafy dark green vegetables, citrus fruits and juices, and lentils, so most women probably get an adequate amount.

For women who have epilepsy, however, some doctors recommend a larger dose, up to 4 mg per day. The seizure medicines phenytoin (Dilantin, Phenytek), carbamazepine (Tegretol,Tegretol XR Carbatrol) and phenobarbital can cause a deficiency of folic acid by interfering with the way it's absorbed. Women who take more than one seizure medicine may be advised to take higher doses. The same applies to women who take at least 1,000 mg per day of Depakote (valproate).

Doctors also recommend higher doses of folic acid (up to 4 mg per day, usually) for women who have children in their family with a neural tube defect, since genetic factors may play a role.

Women who start taking a high dose of folic acid along with phenytoin (Dilantin or Phenytek) should have the level of phenytoin in their blood checked to see whether the folic acid is causing the level of phenytoin to be lower than expected. Having a low blood level of the seizure medicine could increase the risk of seizures.

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed: 11/20/06