Anencephaly is a birth defect in which the brain and bones of the skull don’t form completely while the baby is in the womb. As a result, the baby’s brain, particularly the cerebellum, develops minimally. The cerebellum is the part of the brain primarily responsible for thinking, movement, and senses, including touch, vision, and hearing.

Anencephaly is considered a neural tube defect. The neural tube is a narrow shaft that normally closes during fetal development and forms the brain and spinal cord. This usually happens by the fourth week of pregnancy, but if it doesn’t, the result can be anencephaly.

This incurable condition affects about three pregnancies per 10,000 in the United States each year, according to the Centers for Disease Control (CDC). In about 75 percent of cases, the baby is stillborn. Other babies born with anencephaly may only survive a few hours or days.

In many cases, a pregnancy involving a neural tube defect ends in miscarriage.

The cause of anencephaly is generally unknown, which can be frustrating. For some babies, the cause may be related to gene or chromosome changes. In most cases, the baby’s parents have no family history of anencephaly.

A mother’s exposure to certain environmental toxins, medications, or even foods or beverages may play a role. However, researchers don’t know enough about these potential risk factors yet to provide any guidelines or warnings.

Exposure to high temperatures, whether from a sauna or hot tub or from a high fever, may raise the risk of neural tube defects.

The Cleveland Clinic suggests certain prescription drugs, including some of those used to treat diabetes, may increase the risk for anencephaly. Diabetes and obesity may be risk factors for pregnancy complications, so it’s always ideal to talk with your doctor about any chronic conditions and how they may affect your pregnancy.

One important risk factor related to anencephaly is inadequate intake of folic acid. A lack of this key nutrient may raise your risk of having a baby with other neural tube defects in addition to anencephaly, such as spina bifida. Pregnant women can minimize this risk with folic acid supplements or diet changes.

If you’ve had an infant with anencephaly, your chance of having a second baby with the same condition or a different neural tube defect increases by 4 to 10 percent. Two previous pregnancies affected by anencephaly increase the recurrence rate to about 10 to 13 percent.

Doctors can diagnose anencephaly during pregnancy or immediately after the baby is born. At birth, the abnormalities of the skull can be easily seen. In some cases, part of the scalp is missing, along with the skull.

Prenatal tests for anencephaly include:

  • Blood test. High levels of the liver protein alpha-fetoprotein can indicate anencephaly.
  • Amniocentesis. Fluid withdrawn from the amniotic sac surrounding the fetus can be studied to search for several markers of abnormal development. High levels of alpha-fetoprotein and acetylcholinesterase are associated with neural tube defects.
  • Ultrasound. High-frequency sound waves can help create images (sonograms) of the developing fetus on a computer screen. A sonogram may show the physical signs of anencephaly.
  • Fetal MRI scan. A magnetic field and radio waves produce images of the fetus. A fetal MRI scan provides more detailed pictures than an ultrasound.

The Cleveland Clinic suggests prenatal testing for anencephaly between the 14th and 18th weeks of pregnancy. The fetal MRI scan take place any time.

The most noticeable signs of anencephaly are the missing parts of the skull, which are usually the bones in the back of the head. Some bones on the sides or front of the skull may also be missing or poorly formed. The brain also isn’t formed properly. Without a healthy cerebellum, a person can’t survive

Other signs may include a folding of the ears, a cleft palate, and poor reflexes. Some infants born with anencephaly also have heart defects.

There is no treatment or cure for anencephaly. An infant born with the condition should be kept warm and comfortable. If any parts of the scalp are missing, exposed parts of the brain should be covered.

The life expectancy of an infant born with anencephaly is no more than a few days, more likely a few hours.

Anencephaly is one of several conditions known as cephalic disorders. They’re all related to problems with the development of the nervous system.

One disorder similar to anencephaly in some ways is microcephaly. A baby born with this condition has a smaller-than-normal head circumference.

Unlike anencephaly, which is apparent at birth, microcephaly may or may not be present at birth. It can develop within the first few years of life.

A child with microcephaly may experience normal maturing of the face and other parts of the body, while the head remains small. Someone with microcephaly may be developmentally delayed and face a shorter lifespan than someone without a cephalic condition.

While having one child develop anencephaly can be devastating, keep in mind that the risk of subsequent pregnancies turning out the same way is still very low. You can help reduce that risk even further by making sure you consume sufficient folic acid before and during your pregnancy.

The CDC works with the Centers for Birth Defects Research and Prevention on studies exploring improved methods of prevention and treatment for anencephaly and the entire spectrum of birth defects.

If you’re pregnant or are planning to become pregnant, talk with your doctor soon about all the ways you can help improve the odds of having a healthy pregnancy.

Preventing anencephaly may not be possible in all cases, though there are some steps that may lower the risks.

If you’re pregnant or could get pregnant, the CDC recommends a daily intake of at least 400 micrograms of folic acid. Do this by taking a folic acid supplement or by eating foods fortified with folic acid. Your doctor may recommend a combination of both approaches, depending on your diet.