anencephaly

a failure in the development of a foetus, resulting in the absence of the cerebral hemispheres of the brain and some skull bones. If the pregnancy goes to term, the infant dies soon after birth, but spontaneous abortion occurs in about 50 percent of affected pregnancies. Anencephaly is often associated with SPINA BIFIDA and is the most common developmental defect of the CENTRAL NERVOUS SYSTEM . Anencephaly can be detected during pregnancy by measuring the amount of ALPHA FETOPROTEIN present. See also AMNIOCENTESIS .