Folic acid and neural tube defect: can't we come to closure?

In a series of nonrandomized and randomized intervention trials and case-control and cohort studies, women using multivitamins or folic acid supplements during the first 6 weeks of pregnancy experienced a three- to fourfold reduction in neural tube defects among their offspring. Viewed collectively, these data provide strong evidence that an important subset of US women do not receive sufficient folic acid to minimize their risk of a defective pregnancy. Further, the amounts of folic acid contained in multivitamins (usually 200-400 micrograms per day) appear adequate to greatly reduce, and probably eliminate, the excess risk.