The absence of both the skull and cerebral portions of the brain.

Alternative Names

Aprosencephaly with open cranium

Causes, incidence, and risk factors

Anencephaly is a "neural tube defect" (a defect occurring early in fetal development that damages the primitive tissue which will become the brain and spinal cord). When the upper portion of the neural tube fails to close, anencephaly results, however, the specific cause is unknown. Findings suggest that it may be related to environmental toxins ; however, no absolute connections have been made. Also, low plasma levels of folic acid have been implicated in contributing to neural tube defects. The incidence may reach 3.6 to 4.6 out of 10,000 births. The exact incidence is unknown, as most of these infants probably spontaneously abort. Risk factors include having a previous pregnancy with anencephaly. Nutrition is thought to play an important part in the development of neural tube defects of which anencephaly is only one. The specific nutrition risk factor is thought to be low serum levels of folic acid.

Signs and tests


  • polyhydramnios
  • (this condition is seen prior to delivery)
  • Tests:
  • prepregnancy serum
  • folic acid test
  • amniocentesis
  • (done on the mother to determine if increases levels of alpha-fetoprotein are present)
  • elevated
  • alpha fetoprotein levels during pregnancy (increased levels are suggestive of a neural tube defect)
  • urine estriol levels during pregnancy
  • ultrasound, pregnancy
  • studies -- confirms the diagnosis
  • Treatment

    No specific therapy is recommended. This is a terminal condition.

    Expectations (prognosis)

    This condition is usually fatal within days. There is an increased incidence of neural tube defects in infants born following the prior birth of an anencephalic infant.


    Anencephaly is a fatal disease.

    Calling your health care provider

    This condition is usually found by the physician during routine prenatal testing and ultrasound . If not, then it is noticed immediately upon birth of the infant.


    Increasing the intake of folic acid for at least three months before becoming pregnant and during the first month of pregnancy reduces the risk of some neural tube defects. Centers for Disease Control and the National Institute of Health believe that assuring normal serum folic acid levels can reduce the incidence of neural tube defects by 50 percent. The federal government has passed a national bill that requires grain products such as flour and pasta to be supplemented with folic acid. Therapeutic abortion may be considered following counseling after early in utero detection of anencephaly.

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