Defect, neural tube: A major birth defect caused by abnormal development of the neural tube, the structure present during embryonic life which gives rise to the central nervous system -- the brain and spinal cord. Neural tube defects (NTDs) are among the most common birth defects that cause infant mortality (death) and serious disability.

There are a number of different types of NTDs including anencephaly, spina bifida, and encephalocele. In anencephaly there is absence of the cranial vault (the skull) and absence of most or all of the cerebral hemispheres of the brain. Encephalocele is a hernia of part of the brain and the meninges (the membranes covering it) through a skull defect. spina bifida is an opening in the vertebral column encasing the spinal cord. Through this opening, the spinal cord and the meninges may herniate to create a meningomyelocele.

All pregnancies are at risk for an NTD. However, women with a history of a previous pregnancy resulting in a fetus with an NTD are at higher risk. So are women with a close relative (brother, sister, niece, or nephew) who has an NTD, women with type 1 diabetes mellitus, women with seizure disorders being treated with valproic acid or carbamazepine, and women or their partners who themselves have an NTD.

Landmark research has revealed that 50 percent or more of NTDs could be prevented if women consume a folic acid-containing supplement before and during the early weeks of pregnancy in addition to the folate in their diet. The US Public Health Service, Centers for Disease Control and Prevention (CDC), and American Academy of Pediatrics recommend that all women of childbearing age who are capable of becoming pregnant should consume 400 (0.4 mg) µg of folic acid daily. Because the risk for NTDs is not totally eliminated by folic acid use, routine prenatal screening for NTDs is still advisable.