It is clear that women who take multivitamins that include folic acid lower their risk of having an infant with a neural tube defect (NTD). As part of a public health campaign carried out in the mid-1990s in China, pregnancy outcomes were examined when women were asked to take a pill containing 400 μg of folic acid daily from the time of the premarital examination to the end of the first trimester. The study focused on two regions, one with high and one with low rates of NTDs. In all, NTDs were sought in the fetuses or infants of 130,142 women who took folic acid any time before or during pregnancy and in 117,689 others whose mothers had no taken folic acid at all.
A total of 102 NTDs were found when folic acid had been taken, and 173 were found when women did not take folic acid. For fetuses or infants of women who registered before their last menses and did not take any folic acid, NTDs occurred at a rate of 4.8 per 1000 pregnancies (of 20 weeks' or more gestation) in the high-NTD area and 1.0 per 1000 in the low-NTD region. The rates when women used folic acid periconceptionally were 1.0 and 0.6 per 1000 pregnancies, respectively. The risk of an NTD was lowered the most, 85 percent, for offspring of women in the high-NTD region who took more than 80 percent of their folic acid pills. In the low-NTD area, the risk reduction was 40 percent. The rates of NTD were 0.7 and 0.6 per 1000 pregnancies, respectively. In the high-risk region, the chance of an NTD was half of that for offspring of women who were compliant no more than 80 percent of the time.
The implication of the results of this survey is that the intake of 400 μg of folic acid daily during the periconceptional period can lower the risk of NTDs regardless of whether the risk level in a given geographic area is high or low.
N Engl J Med 1999;341:1485-1490