Folic acid and neural tube defects

Abstract

Major congenital anomalies occur in 2% to 3% of live births. Neural tube defects (NTDs), cleft lip and palate, and cardiac anomalies are some of the most common. NTDs are a group of serious birth defects that affect the developing nervous system and include anencephaly, spina bifida, and encephalocele. Birth records suggest that about 2500 babies with these birth defects, or 1 to 2 per 1000, are born each year in the United States. Some affected pregnancies are spontaneously or electively aborted. Over 95% occur to women without a prior family history of this disorder. Neural tube defects occur within 1 month of conception. Anencephaly and spina bifida are the most common NTDs and occur with about equal frequency, whereas encephalocele is seen less frequently. In anencephaly, there is partial or complete absence of the skull bones usually with a remnant of brain: it is almost always fatal before or shortly after birth. Spina bifida with meningomyelocele results from failure of the vertebral arches to close over an open neural tube defect, exposing the spinal cord and nerves. Although most cases of spina bifida are open, 10% to 15% are closed or covered by skin. Spina bifida is compatible with survival although in most cases individuals have moderate to severe disabilities and, in some cases, may have mental retardation. With encephalocele there is protrusion of the brain and/or its covering membranes through the skull, most often in the occipital region. Folic acid supplementation has been shown to reduce the incidence and recurrence of NTDs and possibly reduce the occurrence of several other birth defects such as cardiac, orofacial, limb, and renal anomalies (see