The association between folic acid intake and risk of congenital heart defects was assessed in 899 women who presented for prenatal care at about 10 weeks’ gestation and 985 other women referred for fetal echocardiography. After adjustment for age, race, binge drinking, smoking, and other potential confounding variables, women who took a daily folic acid supplement during the first 6 weeks of pregnancy (the period during which the heart develops) were 54% less likely to have a baby with one of these defects, compared with women who did not take a daily folic acid supplement. The protective effect of folic acid increased with increasing daily doses of the vitamin, and it appeared that at least 400 mcg/day of supplemental folic acid was necessary to achieve a reduction in risk. No benefit was associated with starting the supplement after 6 weeks’ gestation or with taking folic acid before, but not during, pregnancy. Analysis of stored blood samples showed that the maternal plasma folate level was inversely associated with risk.

Comment: Previous studies have demonstrated that folic acid supplementation around the time of conception greatly reduces the risk of neural-tube defects. Congenital heart defects such as conotruncal defect and ventricular septal defect are much more common than neural tube defects. The results of this new study suggest that supplementation with at least 400 mcg/day of folic acid during the first 6 weeks of pregnancy can reduce the risk of congenital heart defects. As different organs develop at different times during pregnancy, it makes sense for women of childbearing age to take a folic acid-containing multivitamin prior to, and for the entire duration of, pregnancy.

Jancin B. Folic acid slashes risk of congenital heart defects. Fam Pract News 2003(Dec. 15):10.