Preventing neural tube defects: the importance of periconceptional folic acid supplements

To inform the obstetrician-gynecologist of recent scientific evidence regarding the use of supplemental folic acid for prevention of neural tube defects (NTDs).

We selected English language articles via MEDLINE published from January 1990 through February 1997, using the search terms "folic acid" and "neural tube defect." Additional sources were identified through cross-referencing and through searching selected journals published from March through October 1997.

Articles were selected on the basis of their relevance to the relationship between folate intake and NTD incidence, mechanisms of folate responsive NTD formation, and folate provision strategy. We referenced 55 papers in total.

The majority of evidence demonstrates a decreased incidence of NTDs with increased folic acid consumption. The most convincing trials were performed in Europe among women who were planning pregnancy by using multivitamin or folic acid supplements. Some studies suggest that the protective effect of folate is explained, in many cases, not through correction of dietary deficiencies, but through correction of metabolic defects. Other evidence implies that it reduces NTDs by causing abortion of affected conceptuses. Supplemental folic acid tablets are the most proven means of improving an individual's folate status, but ensuring compliance with a strategy using vitamin tablets is problematic.

Women of reproductive age should be advised to take multivitamin supplements containing 0.4 mg folic acid daily. Women with previously affected offspring who intend to become pregnant should take daily supplementation containing 4 mg of folic acid in the periconceptional period to reduce the risk of recurrence.