Q: My sister and I are both pregnant. Her obstetrician has prescribed daily vitamin pills; mine has not. Do pregnant women need nutritional supplements?
A: Most pregnant women do not need vitamin supplements since there is no evidence of benefits in pregnancy, with one possible exception: Many pregnant women can benefit from mineral supplements with iron or calcium or both.
Recent studies show that some women should take folic acid at least a month before they conceive and during the first three months of pregnancy to possibly help prevent neural tube defects.
This has been a subject of considerable investigation. One type of neural tube defect is spina bifida, a failure of the spinal cord to close with the possibility of permanent damage to the spinal cord and spinal nerves. Other neural tube defects include anencephaly, a lethal defect distinguished by absence of most of the brain, and encephalocele, a skull malformation resulting in swelling or ballooning of brain tissue.
Neural tube defects are common and serious; each year about 4,000 infants are born in the United States with the defect. If a woman has had one fetus or infant with a neural tube defect, she has a 2 percent to 3 percent risk of having a similar complication in a subsequent pregnancy.
Although previous studies on the benefits of folic acid during pregnancy have yielded conflicting results, convincing findings were reported from a recent British study. This eight-year study enrolled women who had a fetus or infant with a neural tube defect in a previous pregnancy. The investigators found that a 4 mg tablet of folic acid taken daily before conception and during the first three months of pregnancy reduced the recurrence of neural tube defects by 71 percent. There was no detectable benefit from the addition of a multivitamin pill to the folic acid.
As a result of these findings, the Communicable Disease Center made the following recommendations:
* "Women who have had a pregnancy resulting in an infant or fetus with a neural tube defect should be advised to take 4 mg per day of folic acid starting at the time they plan to become pregnant, from at least 4 weeks before conception through the first 3 months of pregnancy."
* "Multivitamin preparations containing folic acid should not be used to attain the 4 mg dose because harmful levels of vitamins A and D could also be taken."
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine and associate dean for faculty affairs at the school.