What is anencephaly?

Anencephaly, also known as "open skull," is a birth defect in which the major parts of the brain, scalp, and skull of the fetus do not form completely as it is developing in the womb.

Anencephaly occurs when the neural tube, a narrow channel in the fetus that normally closes to form the spinal cord and brain, does not close properly between the third and fourth weeks of pregnancy. An infant born with anencephaly has some or most of the brain missing. These infants are unconscious, cannot feel, and are usually blind and deaf.

In many cases, some brain tissue may be exposed because parts of the skull are missing. Some infants may have a primitive brain stem at birth. They may seem to respond to sound or touch, but their reactions are involuntary and are caused by the action of the brain stem.

Anencephaly is a fatal condition. Infants with anencephaly are stillborn in about 75 percent of cases. Newborns who survive die within several hours, days, or weeks.

What causes anencephaly?

The exact causes of anencephaly are unknown. A lack of folic acid (vitamin B9) before and during pregnancy may increase the chance of neural tube defects, such as anencephaly or spina bifida (a birth defect in which the spine is exposed). If a woman takes certain prescription drugs during pregnancy, such as drugs for diabetes, this may increase the risk of having an infant with anencephaly.

In about 90 percent of cases, the parents of an anencephalic infant do not have a family history of the disorder. However, if the parents have had a child who was born with anencephaly, they have a greater chance of having another baby with this condition. The recurrence rate for anencephaly is 4 to 5 percent, and rises to 10 to 13 percent if the parents have had two other children with anencephaly.

How common is anencephaly?

About one in nearly 5,000 babies is born with anencephaly each year, according to the Centers for Disease Control. The exact number is not known because many pregnancies involving neural tube defects end in miscarriage. More female newborns have anencephaly than males, possibly because of a higher rate of spontaneous abortions or stillbirths among male fetuses.

How is anencephaly diagnosed?

Prenatal tests for anencephaly include:

  • Blood tests: Tests may show high levels of alpha-fetoprotein, a protein produced by the immature liver cells of the fetus.
  • Amniocentesis: A small amount of fluid is withdrawn from the amniotic sac using a long needle that is inserted through the abdomen. The fluid can be analyzed to measure the levels of alpha-fetoprotein and acetylcholinerase. Higher-than-normal levels are linked to neural tube defects, such as anencephaly.
  • Ultrasound: This imaging test uses high-frequency sound waves and a computer to make an image (sonogram) of the developing fetus. Abnormalities linked with anencephaly can be seen on the sonogram.
  • Fetal MRI: This imaging test uses a magnet to generate an image of the developing fetus. The brain and its various structures can be seen in more detail than the ultrasound alone.

Any of these procedures may be performed between the 14th and 18th weeks of pregnancy. The fetal MRI can be performed at any point of the pregnancy.

After a baby with anencephaly is born, the diagnosis is more apparent since the abnormalities of the skull can be easily seen. Bones around the front and sides of the head or the bony covering in the back of the head may be missing. Some brain tissue may be exposed when parts of the skull or scalp are missing.

How is anencephaly treated?

There is no treatment for anencephaly; instead, the child is provided with supportive care. The infant should be kept warm and any areas of the brain that are exposed must be protected. Sometimes a special bottle is used to help feed babies who may have difficulty swallowing fluids.

How can anencephaly be prevented?

Methods for preventing anencephaly include the following:

  • Proper nutrition: Eating nutritious foods and taking a vitamin supplement before and during pregnancy may help prevent neural tube birth defects. Getting enough folic acid is very important. Women of childbearing age should take a daily multivitamin supplement with at least 400 micrograms of folic acid, since most women do not obtain enough folic acid from food alone. The synthetic form of the vitamin is more easily absorbed and utilized by the body than the form which occurs naturally in foods.

    Other good sources of folic acid include leafy green vegetables, dried beans, oranges, and orange juice. Some products are fortified with folic acid, including enriched flour, rice, bread, pasta, and cereals. The U.S. Food and Drug Administration requires that folic acid be added to all enriched cereal grain products.

  • Folic acid supplements: Pregnant women who have previously given birth to an infant with a neural tube defect may have to take higher amounts of folic acid during pregnancy. Women should talk to their doctors about the recommended amount of folic acid. It is suggested that women who have had a previous pregnancy involving a neural tube defect should take 4 mg of folic acid, beginning one to two months before conception through their first trimester of pregnancy, under a doctor's supervision.


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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 1/19/2017…#15032