Efficacy of folic acid prophylaxis for the prevention of neural tube defects

Thirty years ago, researchers suggested that maternal intake of certain vitamins during pregnancy affected the incidence of serious birth defects. Since then, two randomized controlled trials and several observational studies have proven that if women take folic acid during the periconceptional period, they can lower their risk of having children with neural tube defects (NTDs), serious birth defects of the spine and brain. In 1992, the U.S. Public Health Service recommended that all women capable of becoming pregnant take 0.4 mg of folic acid daily. Translating this recommendation into practice, however, presents a major public health challenge. In 1996, the U.S. Food and Drug Administration ruled that "enriched" cereal grain products must be fortified with folic acid, the first time food has been fortified for the prevention of birth defects. However, because the level chosen for folic acid fortification will not provide all women the optimal protection against the occurrence of NTDs, efforts to increase reproductive-age women's consumption of folic acid-containing vitamins and folate-rich foods are underway The mechanism underlying folic acid's efficacy in preventing NTDs is unknown. It may work by correcting a deficiency or by overcoming an inherited disorder of folate metabolism. The role of genetics and agents such as vitamin B-12, methionine, and homocysteine in NTD prevention, and the relationship of these factors with folic acid, are under investigation. Although the mechanism for folic acid's protective effect is unknown, it is clear that a significant proportion of NTDs can be prevented and that prevention efforts should not await the elucidation of specific mechanisms, (C) 1998 Wiley-Liss. Inc.