Folic acid supplementation and risk for imperforate anus in China.

Maternal consumption of folic acid before pregnancy and during early pregnancy is associated with a reduced risk for some birth defects. Whether folic acid can reduce the risk for imperforate anus is unknown. As part of a public health campaign conducted in China from 1993 through 1995, the outcomes of pregnancies of > or =20 weeks' gestation were evaluated among women using folic acid supplements. The women were asked to take one pill containing 400 microg of folic acid (without other vitamins) every day from the time of their premarital examination until the end of their first trimester of pregnancy. Rates of imperforate anus and risk ratios for imperforate anus among the offspring of these women were calculated according to folic acid use. Among the offspring of women who took folic acid and women who did not take folic acid, 20 and 30 infants with imperforate anus were identified, respectively. The rate of imperforate anus was 3.1 per 10,000 among the offspring of women who did not take folic acid and 1.6 per 10,000 among the offspring of women who took folic acid; adjusted for maternal age, the risk ratio was 0.59 (95% confidence interval: 0.33, 1.07). Daily maternal consumption of 400 microg of folic acid before and during early pregnancy may reduce the risk for imperforate anus.