Anencephaly is a fatal birth defect. It occurs when the fetal brain and skull don’t develop in your uterus as expected. Babies born with the condition die within a few hours or days. Most pregnancies end in miscarriage. You can lower your risk by taking the recommended dose of folic acid before and during pregnancy.


What is anencephaly?

Anencephaly is a birth defect (congenital disorder) where a baby is born without parts of their brain and skull.

This condition affects a baby’s nervous system, which includes their brain, spine and nerves. It happens when the neural tube (which is responsible for growing the brain, skull, backbones and spinal cord) doesn’t develop or fails to close as it should in the first month of pregnancy. That’s why anencephaly is a type of cephalic disorder called a neural tube defect.

The brain is essential to survival. It controls body functions, emotions and memory. Since anencephaly affects how the brain develops, babies born with anencephaly usually live only a few minutes, hours or days. Most pregnancies with anencephaly end in miscarriage or stillbirth.

What are the types of anencephaly?

There are three types of anencephaly and all three are fatal for the fetus:

  • Meroanencephaly: The brainstem and midbrain only partially develop. Some skin and skull cover the brain.
  • Holoanencephaly: The brain didn’t develop at all. This is the most common type.
  • Craniorachischisis: The brain, skull and spine didn’t develop. This is the most severe type.

How common is anencephaly?

Anencephaly is a common type of neural tube defect. Studies estimate it happens in 1 in 1,000 pregnancies. But since most anencephaly pregnancies end in miscarriage, the condition only affects an estimated 1 in 10,000 newborns in the United States.


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Symptoms and Causes

What are the signs of anencephaly?

Signs of anencephaly include:

  • High levels of alpha-fetoprotein (a fetal protein) from a blood test or sample of amniotic fluid of the pregnant parent. This blood test is usually done in the second trimester of pregnancy.
  • Too much fluid in the amniotic sac (polyhydramnios) may be seen during a prenatal ultrasound.
  • Missing parts of the skull and brain.
  • Exposed areas of brain tissue (no skin or skull covering it).
  • Smaller head size than expected.

A healthcare provider will offer tests to detect conditions like anencephaly during pregnancy.

What are the symptoms of anencephaly?

The birthing parent may not be aware of any symptoms until a blood test or an ultrasound.

Newborns with anencephaly don’t have:

  • Consciousness (awareness).
  • Vision.
  • Hearing.
  • The ability to feel pain.

Not all newborns with anencephaly develop a brainstem. If they do, they may have reflexes and automatically respond to touch. Seeing your newborn respond like this might give you hope. But this isn’t a sign that they’re aware of your touch or that they’ll be able to live long-term with this condition.


What causes anencephaly?

A problem with how the neural tube forms and closes causes anencephaly. The neural tube is a flat piece of tissue that grows into a tube shape. Each part of the neural tube helps parts of a baby’s body grow:

  • Brain and skull (top of the neural tube).
  • Spinal cord (middle of the neural tube).
  • Backbones (bottom of the neural tube).

Anencephaly happens when the top part of the neural tube doesn’t close during embryonic development. This occurs during the third and fourth week of pregnancy. The fetus continues to form, except the front of the brain (forebrain) and the top of the brain (cerebrum) don’t grow. Other parts of the brain may develop as expected but no skin or skull cover them.

Is anencephaly inherited?

As far as we know, anencephaly isn’t inherited (passed down in families). In most cases, it occurs without any family history of the condition (sporadic genetic mutation). But if you had a child with a neural tube defect (NTD) before, like spina bifida, you have a higher chance of having a baby with anencephaly. This risk is about 2% to 3 %, which is 20 times higher than in someone who hasn’t had a previous baby with spinal bifida.

What are the risk factors for anencephaly?

Certain medications and risk factors increase the chance of having a baby with anencephaly or another neural tube defect (NTD) including:

  • Lack of folic acid: Not getting enough folic acid (vitamin B9) when you’re pregnant puts you at a higher risk of having a baby with anencephaly. A healthcare provider may recommend you take a prenatal vitamin with 400 micrograms (mcg) of folic acid before and during pregnancy.
  • Diabetes: Changes to blood glucose levels (sugar in your blood) can be dangerous for a developing fetus. A healthcare provider can help you manage a diabetes diagnosis to reduce your risk of complications.
  • Medications: Antiseizure medications such as phenytoin (Dilantin®), carbamazepine (Tegretol®) and valproic acid (Depakote®) can increase your risk of having a baby with NTDs. Some of these medications also treat migraines and bipolar disorder. Talk to your healthcare provider about the medications you currently take if you plan on becoming pregnant. Don’t stop taking medication unless your healthcare provider approves it.
  • Opioid use: Taking opioids during the first two months of pregnancy can cause NTDs. Opioids may include heroin and prescription painkillers, such as hydrocodone.

Diagnosis and Tests

How is anencephaly diagnosed?

When you’re pregnant, you’ll have certain prenatal screening tests that can detect birth defects and other conditions that might affect the health of the fetus. Prenatal tests that can diagnose anencephaly include:

  • Quad marker screen: This blood test checks for neural tube defects and other genetic conditions. Your provider takes a sample of your blood and sends it to a lab. One of the tests in the quad marker screen (which tests four markers in the pregnant parent’s blood ) is the 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. AFP can also be drawn on its own without having other tests.
  • 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.

A healthcare provider may diagnose anencephaly after a baby is born if you opt out of prenatal screening tests, including ultrasounds. This happens during your newborn’s physical exam.

How early can anencephaly be detected?

A healthcare provider may be able to detect anencephaly after eight to 12 weeks in the first trimester. On average, screenings for anencephaly usually happen around 18 to 20 weeks.


Management and Treatment

How is anencephaly treated?

There’s no available cure or treatment for anencephaly. Almost all babies born with anencephaly die within a few hours or days after birth. Your newborn’s healthcare providers will support you and help you grieve and say goodbye.


Can anencephaly be prevented?

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

  • Getting 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) happen in the first month of pregnancy — before you even know you’re pregnant. So, it’s essential to start taking folic acid before you start trying to conceive. If you’ve had a child with an NTD, talk to your healthcare provider about steps you can take to prevent future NTDs. Usually, a higher dose of folic acid is recommended.
  • Discussing changes to your medications with a healthcare provider: Certain medications that regulate seizures and other conditions may cause birth defects like NTDs. Ask your provider about the medications you’re taking if you plan on becoming pregnant.
  • Managing your health: If you have an underlying health condition, like diabetes, talk to your healthcare provider about ways to manage the condition so you can stay in good health.

Outlook / Prognosis

What’s the outlook for anencephaly?

Anencephaly is a fatal condition with a very poor outlook. Most fetuses with anencephaly pass away before birth, and the pregnancy ends in miscarriage. Almost all babies born with anencephaly die within a few minutes, hours or days.

Does a newborn with anencephaly feel pain?

You may worry that your newborn is distressed, uncomfortable or in pain, but babies with anencephaly can’t feel pain. Infants who survive birth may seem to respond to touch or sound. But they aren’t really responding to feeling or sound because they don’t have the largest part of their brain (cerebrum), which allows them to move, think, feel and respond.

Living With

How do I take care of myself after losing a child to anencephaly?

Learning that your baby has anencephaly is extremely difficult. Your care team will help you and your loved ones say goodbye and provide follow-up care to make sure you and your family are doing as well as you possibly can after the loss of a child.

You may find that you need support or someone to talk to. If so, your healthcare team can connect you to a mental health professional or a bereavement support group where you can share your feelings with others who’ve had similar losses. It’s understandable if you feel heartbroken and hopeless, but surrounding yourself with a network of support can help you with any grief you’re feeling.

When should I see a healthcare provider?

If you’re planning to become pregnant, start with a preconception counseling visit. A healthcare provider can help you maintain good health to lower your risk of having a child with a birth defect.

If you’re having any symptoms of a miscarriage, like heavy bleeding, cramps and/or severe back or abdominal pain, contact your pregnancy care provider right away.

What questions should I ask my healthcare provider?

  • How do I stay healthy during pregnancy?
  • Will the medications I currently take affect a fetus if I become pregnant?
  • Do I need to take folic acid, and if so, how much and how often?
  • What steps should I take if I want to become pregnant again after having a child with a neural tube defect?
  • Can you recommend a support group or a mental health professional to help with grief?
  • How do I take care of myself after losing a child?

A note from Cleveland Clinic

Severe birth defects are still possible even if you’ve done everything your healthcare provider recommends to have a healthy pregnancy. Anencephaly is an extremely devastating diagnosis to hear. Your healthcare team will be beside you to answer all your questions and help you come to terms with the loss. It may help to find comfort in talking with a mental health professional, joining a support group or surrounding yourself with a close network of friends and family.

Medically Reviewed

Last reviewed on 08/29/2023.

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