Neural tube defects (NTDs) are serious birth defects that result from the failure of the neural tube to close in the cranial region (anencephaly) or more caudally along the spine (spina bifida) by the 28th day of gestation. Infants born with anencephaly usually die within a few days of birth, and those with spina bifida have life-long disabilities with varying degrees of paralysis. Currently, identified risk factors for NTDs include a mother who previously had an NTD-affected pregnancy, maternal diabetes, obesity, hyperthermia, certain antiseizure medications, genetic variants, race/ethnicity, and nutrition (particularly folic acid insufficiency). In the United States, during 1995-1996, approximately 4,000 pregnancies were affected by an NTD. This number declined to 3,000 pregnancies in 1999-2000 after fortification of enriched cereal grain products with folic acid was mandated. Worldwide, in 1998, approximately 300,000 births were affected by an NTD.