What is anencephaly?

Anencephaly is a birth defect (a health problem identified at birth). It occurs when the skull, scalp and brain do not develop properly in your uterus. Portions of the fetal brain and skull are missing. The brain tissue that does form is usually exposed because there isn’t enough skin and bone to cover it.

Birth defects in the nervous system (the brain, spine and nerves), like anencephaly, are neural tube defects (NTDs). Neural tube problems develop very early in pregnancy. Babies born with anencephaly live only a few hours or days after birth.

How common is anencephaly?

About one out of every 5,000 to 10,000 babies is born with anencephaly, and the condition affects baby girls more often than boys. Most pregnancies with anencephaly end in miscarriage or stillbirth. People who have had another child with an NTD, such as spina bifida, have a higher risk of conceiving a child with anencephaly.

Symptoms and Causes

What causes anencephaly?

Anencephaly doesn’t appear to be inherited (passed down in families). In most cases, it occurs without any family history of the condition. But if you’ve had a child with a neural tube defect (NTD) before, you have a higher chance of having a baby with anencephaly.

A combination of environmental factors, genes and nutrition during pregnancy likely causes anencephaly. Certain drugs and risk factors increase the chance of having a baby with anencephaly or another NTD, including:

  • Lack of folic acid: Women who don’t get enough folic acid (vitamin B9) when they’re pregnant have a higher risk of having a baby with anencephaly. Women should take a prenatal vitamin with 400 micrograms (mcg) of folic acid before and during pregnancy.
  • Diabetes: Unmanaged diabetes increases the risk of NTDs. It causes blood glucose levels (sugar in the blood) to get too high and harm fetal development.
  • High body temperature: Having a fever or using a hot tub or sauna during early pregnancy can increase your risk of having a baby with an NTD.
  • Medications: Anti-seizure drugs such as phenytoin (Dilantin®), carbamazepine (Tegretol®) and valproic acid (Depakote®) can cause NTDs. Some of these drugs also treat migraines and bipolar disorder.
  • Obesity: People who had obesity before pregnancy have a higher chance of having a baby with anencephaly or another NTD.
  • Opioid use: Taking opioids during the first two months of pregnancy can cause NTDs. Opioids include heroin (an illegal drug) and prescription painkillers such as hydrocodone.

How does anencephaly occur?

Sometimes called “open skull,” anencephaly happens when the upper part of the neural tube doesn’t close completely during fetal development. The neural tube is a flat piece of tissue that grows into a tube and forms the brain and spinal cord. Without a closed tube, the brain and skull don’t develop.

Like all neural tube defects, anencephaly occurs during the third and fourth weeks of pregnancy. The fetus continues to form and grow as the pregnancy progresses.

Diagnosis and Tests

How is anencephaly diagnosed?

During pregnancy, your healthcare provider may order tests to look for signs that might indicate a neural tube defect. Providers can also diagnose anencephaly at birth based on the newborn’s appearance. Prenatal tests for anencephaly include:

  • Quad marker screen: This blood test checks for neural tube defects and genetic disorders. Your provider takes a sample of your blood and sends it to a lab for testing. One of the tests in the quad marker screen is for alpha-fetoprotein (AFP). The AFP test detects higher levels of this protein. The fetal liver makes AFP, and high levels leak into a pregnant person's blood if anencephaly is present.
  • Ultrasound: Using sound waves, this imaging test produces pictures of the fetus. Your provider uses an ultrasound (sonogram) to look at the fetal skull, brain and spine.
  • Fetal magnetic resonance imaging (MRI): To see the brain and spine in greater detail, your provider may order this imaging test. An MRI uses high-powered magnets to produce images of tissues and bones.
  • Amniocentesis: Your provider inserts a thin needle into the amniotic sac (the fluid-filled bubble around the fetus in your uterus) and withdraws some fluid. A lab checks the amniocentesis fluid for high levels of AFP and an enzyme called acetylcholinesterase. Either of these substances may mean a fetus has a neural tube defect.

Management and Treatment

Can anencephaly be treated?

Healthcare providers cannot treat anencephaly. Almost all babies born with anencephaly die within a few hours or days after birth. Providers work compassionately with families to help them say goodbye.


How can I prevent anencephaly?

Although it isn’t always possible to prevent anencephaly, you may be able to reduce your chance of having a child with the condition. To lower your risk, you should:

  • Get plenty of folic acid: Take 400 mcg of folic acid daily, even if you don’t plan to get pregnant right away. Neural tube defects (NTDs) occur in the first month of pregnancy, so it’s essential to start taking folic acid before you plan to become pregnant. If you’ve had a child with an NTD, talk to your provider about taking more than 400 mcg of folic acid.
  • Avoid certain medications: Drugs that control seizures and treat migraines and bipolar disorder can cause NTDs. Ask your provider about medications you’re taking before you become pregnant. Don’t take opioids if you think you may be pregnant.
  • Stay out of saunas and hot tubs: To keep your body temperature from getting too high, never go into a sauna or hot tub if you think you might be pregnant. If you have a fever while pregnant, ask your provider about taking acetaminophen (Tylenol®) to reduce your temperature.
  • Manage your health: Try to lose weight before you conceive if you have obesity, and maintain a healthy weight during pregnancy. If you have diabetes, talk to your provider about how to safely manage diabetes during pregnancy

Outlook / Prognosis

What is the outlook for babies who have anencephaly?

Anencephaly is a fatal condition. Most fetuses with anencephaly pass away before birth, and the pregnancy ends in miscarriage. Babies born with anencephaly die within a few hours, days or weeks.

Infants who survive at birth may seem to respond to touch or sound, but these responses are involuntary. Newborns with anencephaly are unconscious, blind and deaf. You may worry that your baby is distressed or uncomfortable, but babies with anencephaly cannot feel pain.

Living With

What questions should I ask my provider about anencephaly?

If you’re planning to get pregnant, ask your healthcare provider what you can do to lower your risk of having a baby with anencephaly. Ideally, talk to your provider long before you become pregnant so you can make a plan together.

If you have had a child with a neural tube defect, talk to your provider before getting pregnant again. Your provider may recommend taking more folic acid (4,000 mcg instead of 400 mcg) to reduce your risk of having another baby with a neural tube defect. But taking too much folic acid can be dangerous, so be sure to follow your provider’s guidelines.

A note from Cleveland Clinic
It isn’t always possible to prevent anencephaly and other neural tube defects. But by planning ahead and staying healthy, you can significantly lower your risk of having a baby with the condition. If you’re of childbearing age, you should take 400 mcg of folic acid every day, even if you don’t plan to become pregnant. Talk to your provider about how you can stay healthy, especially if you’ve had a child with a neural tube defect before.

Last reviewed by a Cleveland Clinic medical professional on 08/18/2020.


  • Centers for Disease Control. Facts About Anencephaly. ( Accessed 8/19/2020.
  • March of Dimes Foundation. Neural Tube Defects. ( Accessed 8/19/2020.
  • National Institutes of Health. Anencephaly. ( Accessed 8/19/2020.
  • National Organization for Rare Disorders. Anencephaly. ( Accessed 8/19/2020.

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