Anencephaly

What is anencephaly?

Anencephaly is a serious birth defect in which a large part of a baby’s brain, skull, and scalp does not develop. It belongs to a group of conditions called neural tube defects. The neural tube is a narrow channel of cells that forms in the first weeks of pregnancy and later becomes the brain and spinal cord. In anencephaly, the upper (head) end of this tube fails to close as it should. As a result, the parts of the brain that control thinking, seeing, hearing, and movement are missing or severely underdeveloped, and the bones of the skull that would normally cover them do not form.

Anencephaly affects the developing baby, not the mother. It happens very early, usually before a woman knows she is pregnant, and it is present from that point onward. The condition is often detected during routine prenatal care, either through blood screening or ultrasound. Because it involves structures that are essential for life, anencephaly is not survivable in the long term, and care focuses on supporting the family and keeping the baby comfortable.

This page explains anencephaly symptoms, anencephaly causes, how anencephaly diagnosis is made, and what anencephaly treatment and support usually involve. It is intended for general information and does not replace a conversation with your own care team.

Anencephaly symptoms and signs

Anencephaly symptoms are best understood in two settings: signs that may appear during pregnancy, and physical features that are seen in the baby at birth or on imaging.

During pregnancy

In many cases, the mother notices nothing unusual. The pregnancy may feel completely normal. Some possible signs that can prompt further checks include:

• An unusually high level of a protein called alpha-fetoprotein (AFP) on a routine maternal blood screening test.
• Polyhydramnios, which means too much amniotic fluid (the fluid that surrounds the baby). This can occur because a baby with anencephaly may not swallow fluid normally.
• Findings on a routine ultrasound scan that show the top of the skull and brain are not forming.

In the baby

The physical signs of anencephaly are usually clear and include:

• Absence of a large portion of the skull, scalp, and brain, especially the front and top of the head.
• Brain tissue that is exposed or covered only by a thin membrane, rather than by bone and skin.
• A flattened or absent forehead, sometimes with the ears appearing low set or folded.
• Facial differences such as a cleft palate (an opening in the roof of the mouth) in some babies.
• Lack of consciousness and no response to light, sound, or touch.
• Possible reflex movements, such as breathing efforts or limb movements, which come from the brain stem or spinal cord rather than from awareness.
• Difficulty breathing and maintaining a normal heart rate after birth.

Types of anencephaly

Doctors sometimes describe subtypes based on how much of the skull and brain is affected. In meroanencephaly, part of the skull is missing and a small amount of disorganized brain tissue may be present. In holoanencephaly, the skull is largely absent and the brain is missing almost entirely. In craniorachischisis, the skull defect continues down the back as an open spine. The terms describe severity of the anatomy, but all forms are considered life-limiting.

Anencephaly causes and risk factors

Anencephaly causes are not fully understood. Most cases are thought to result from a combination of genetic factors and environmental influences acting together during the first few weeks of pregnancy, when the neural tube is closing. In most families there is no single identifiable cause.

Possible contributing causes

• Failure of neural tube closure: the direct cause is that the head end of the neural tube does not close during early development.
• Low folate (folic acid) status: folate is a B vitamin needed for the neural tube to close. Not having enough folate before and during early pregnancy is linked with neural tube defects.
• Genetic factors: variations in genes involved in folate processing and in early development may play a role, although a specific gene change is rarely found.
• Chromosomal conditions: a small number of cases occur alongside changes in the number or structure of chromosomes.
• Certain medications: some anti-seizure medicines and drugs that interfere with folate are associated with a higher risk.

Risk factors

• A previous pregnancy affected by a neural tube defect, such as anencephaly or spina bifida.
• Poorly controlled diabetes before and during early pregnancy.
• Obesity.
• A high fever or overheating (for example, from a hot tub) during the first weeks of pregnancy.
• Use of certain anti-seizure medications in early pregnancy.
• A family history of neural tube defects.

It is important to understand that having one or more of these risk factors does not mean a pregnancy will be affected, and many affected pregnancies occur in women with no known risk factors at all. Nothing a parent did or did not do is usually to blame.

Anencephaly diagnosis

Anencephaly diagnosis is most often made before birth as part of routine prenatal care. Because the anatomical changes are marked, imaging is usually able to show the condition clearly once the pregnancy is far enough along.

Prenatal screening blood tests

Many pregnant women are offered a maternal serum screening test in the second trimester, sometimes called the triple or quadruple screen. One of the substances measured is alpha-fetoprotein (AFP), a protein made by the baby. When the neural tube is open, AFP leaks into the amniotic fluid and then into the mother’s blood, so the level is often higher than expected. A raised AFP is a screening result, not a diagnosis, and it leads to further testing.

Ultrasound

Ultrasound is the main tool for confirming anencephaly. The condition can sometimes be suspected at the first-trimester scan (around 11 to 14 weeks), and it is usually clearly visible at the detailed anatomy scan in the second trimester (around 18 to 22 weeks). The scan shows absence of the top of the skull and brain above the level of the eye sockets. A specialist in maternal-fetal medicine may perform a more detailed scan to confirm the findings and to look for other differences, such as an open spine or heart abnormalities.

Additional tests

• Fetal MRI: magnetic resonance imaging (a scan using magnets and radio waves) may be used in some cases to obtain more detail, although it is not always necessary.
• Amniocentesis: a procedure in which a small sample of amniotic fluid is taken with a fine needle. The fluid can be tested for AFP and an enzyme called acetylcholinesterase, and it can be used for chromosomal analysis.
• Genetic counseling: a genetic counselor may review family history and test results and explain what they mean for this and future pregnancies.

Diagnosis after birth

If the condition was not found during pregnancy, it is evident on physical examination at birth because of the missing skull and exposed brain tissue. No further testing is usually needed to confirm it, although the care team may recommend genetic evaluation to inform future planning.

In hospital groups such as Acibadem, the diagnosis and follow-up of neural tube defects during pregnancy are generally managed by the Perinatology (High-Risk Pregnancy) Department, working alongside genetic counselors and newborn specialists.

Anencephaly treatment and care options

There is no cure for anencephaly and no anencephaly treatment that can replace missing brain tissue or restore function. Surgery cannot rebuild the brain, and medication cannot reverse the defect. Because of this, care is centered on the wellbeing of the baby and the family rather than on correcting the condition. The options below describe what care teams usually discuss.

Counseling and decision support

After a diagnosis, parents are usually offered time with a perinatologist, a genetic counselor, and often a palliative care or psychology team. They explain the diagnosis, answer questions, and discuss the choices available for the pregnancy. Decisions about continuing the pregnancy or not are deeply personal and depend on medical, legal, and individual factors that differ between people and places. Your care team can outline the options that apply to you without pressure.

Care during a continued pregnancy

If a pregnancy continues, it is generally monitored more closely. The team may watch for excess amniotic fluid and plan the timing and place of delivery. A birth plan is often prepared in advance so that everyone involved knows the family’s wishes, including how much medical intervention is wanted for the baby after birth.

Comfort (palliative) care after birth

Palliative care means care that focuses on comfort rather than cure. For a baby with anencephaly, this may include keeping the baby warm, protecting the exposed tissue with a soft dressing, gentle handling, and skin-to-skin contact with parents. Medication may be given if the baby appears uncomfortable. Life-support measures such as mechanical ventilation are generally not recommended because they cannot change the outcome, but families and doctors make these decisions together.

Memory-making and family support

Many hospitals offer support for families to spend time with their baby, take photographs, and create keepsakes. Bereavement counseling, support groups, and religious or spiritual care are often available. Some families choose to explore organ or tissue donation; whether this is possible depends on local rules and the baby’s circumstances, and the care team can explain what applies.

Planning for future pregnancies

Because a previous neural tube defect raises the chance of another, doctors often recommend a higher dose of folic acid before a future pregnancy and closer early monitoring. Your doctor can advise the appropriate dose and timing for your situation.

Living with anencephaly: outlook and what to expect

The outlook for a baby with anencephaly is unfortunately very poor. Some babies are stillborn. Those who are born alive usually live for a short time, often hours to days, because the brain structures needed to control breathing, heart rate, and body temperature are missing or incomplete. Rarely, a baby may live somewhat longer with comfort care, but long-term survival is not expected, and the baby will not gain awareness, sight, hearing, or the ability to feel pain in the way a typically developing child does.

For parents, living with an anencephaly diagnosis often means living with grief, which can begin at the time of the diagnosis and continue long after. Feelings of shock, guilt, anger, and sadness are common and normal. It can help to know that the condition arises in the first weeks of development and is not caused by something a parent did after learning they were pregnant. Counseling, peer support from other families, and follow-up with a perinatology or genetics team can help with both emotional recovery and planning for the future.

Most people who have had a pregnancy affected by anencephaly go on to have healthy pregnancies later, although the risk of a repeat neural tube defect is higher than in the general population. Preconception planning with a doctor, including folic acid supplementation and management of conditions such as diabetes, is generally recommended.

Frequently asked questions

What are the first anencephaly symptoms a pregnant woman might notice?

Often there are none. Most women with an affected pregnancy feel well, and the condition is found through routine screening rather than through symptoms. In some cases the abdomen may grow faster than expected because of excess amniotic fluid, but this has many other causes. If anything about your pregnancy feels different, it is reasonable to mention it to your doctor or midwife.

What causes anencephaly, and could I have prevented it?

Anencephaly causes are usually a mix of genetic and environmental factors, and in most cases no single cause is found. Getting enough folic acid before conception and in early pregnancy is associated with a lower risk of neural tube defects, which is why it is widely recommended. However, anencephaly can still occur in women who took folic acid and followed all advice. It is not the result of a parent’s fault.

How is anencephaly diagnosis confirmed before birth?

Diagnosis usually starts with a raised alpha-fetoprotein level on a maternal blood screen or with findings on a routine ultrasound. It is confirmed by a detailed ultrasound that shows the top of the skull and brain are absent. Amniocentesis or fetal MRI may be added in some situations, but ultrasound alone is often sufficient. A false alarm from the blood test is possible, which is why imaging is used to confirm.

Is there any anencephaly treatment that can help the baby survive?

No. There is currently no surgery, medication, or other treatment that can replace the missing brain and skull or allow long-term survival. Anencephaly treatment is therefore focused on comfort care for the baby and on emotional and practical support for the family. Your care team can explain what comfort measures are available and help you prepare a plan for the time around birth.

Is anencephaly the same as spina bifida?

Both are neural tube defects, meaning the neural tube did not close properly in early pregnancy, but they affect different parts of it. Anencephaly affects the head end, leading to missing brain and skull, and is not survivable. Spina bifida affects the spine and, while it can cause significant disability, many people with spina bifida live long lives with treatment. The two conditions share some risk factors, including low folate.

Will anencephaly happen again in a future pregnancy?

Having one pregnancy affected by a neural tube defect increases the chance of another compared with the general population, but the majority of future pregnancies are not affected. Doctors often recommend a higher dose of folic acid starting before conception, good control of any chronic conditions, and an early detailed ultrasound in the next pregnancy. Genetic counseling can give you a clearer picture based on your own history.

When to see a doctor

If you are pregnant and have not yet had prenatal screening, or if you have a family history of neural tube defects, talk with your doctor about the screening and ultrasound tests available to you. If you have already received an anencephaly diagnosis, regular follow-up with your perinatology team is important so that your pregnancy can be monitored and a birth plan agreed.

Seek urgent medical care during pregnancy if you experience any of the following red-flag signs, which need prompt assessment regardless of the baby’s diagnosis:

• Vaginal bleeding or leaking of fluid from the vagina.
• Sudden, rapid increase in the size of your abdomen, or severe abdominal tightness or pain.
• Regular painful contractions before your expected due date.
• Severe headache, changes in vision, or sudden swelling of the face and hands, which can be signs of high blood pressure in pregnancy.
• Fever, chills, or feeling very unwell.
• Shortness of breath, chest pain, or difficulty lying flat, which can occur with excess amniotic fluid.
• A noticeable change or reduction in your baby’s movements if you have been feeling them.

If your baby has been born with anencephaly and is receiving comfort care at home, contact your care team if the baby appears to be in distress, has trouble breathing that seems uncomfortable, develops a fever, or if the exposed tissue shows signs of infection such as redness, swelling, or discharge. Your team can guide you on comfort measures and next steps.