Anencephaly

Overview

Anencephaly is a serious birth defect in which a baby is born missing major portions of the brain, skull, and scalp. It is one of a group of conditions called neural tube defects, which happen when the neural tube, the early structure that forms the brain and spinal cord, does not close properly in the first weeks of pregnancy.

In anencephaly, the upper part of the neural tube fails to close, so the forebrain and the bones of the upper skull do not develop. Anencephaly is not compatible with long-term survival; most affected pregnancies end in miscarriage or stillbirth, and babies born alive usually live only a short time. Although the outlook is grave, much is known about reducing the risk, particularly through adequate folic acid before and during early pregnancy.

Features

Anencephaly is usually identified before birth through prenatal testing. Its features include:

• Absence of the upper part of the skull and scalp
• Absent or severely underdeveloped forebrain and cerebrum (the thinking part of the brain)
• The brainstem may be present, which can allow basic reflexes for a short time
• Often accompanied by other neural tube or facial differences

Because the parts of the brain responsible for awareness do not form, a baby with anencephaly is permanently unconscious. The condition is diagnosed by its physical appearance and imaging rather than by ordinary symptoms.

Causes

Anencephaly results from failure of the neural tube to close near the head end during the third and fourth weeks of pregnancy, often before a person knows they are pregnant. The exact cause in any individual is usually unknown and is thought to involve a combination of genetic and environmental factors. Contributing factors include:

• Low folic acid (folate): Insufficient folate around conception is a major, preventable risk factor.
• Genetic factors: A family or personal history of neural tube defects increases risk.
• Certain medications and medical conditions: Some anti-seizure drugs and poorly controlled diabetes raise the risk.
• Other factors: Obesity and high body temperature in early pregnancy have been linked to neural tube defects.

Risk Factors

• Inadequate folic acid intake before and during early pregnancy
• A previous pregnancy affected by a neural tube defect
• A family history of neural tube defects
• Poorly controlled diabetes before pregnancy
• Use of certain anti-seizure medications
• Obesity in the parent carrying the pregnancy

Diagnosis

Anencephaly is typically detected during pregnancy through routine prenatal care:

• Maternal blood screening: A blood test may show elevated alpha-fetoprotein (AFP), which can indicate a neural tube defect.
• Ultrasound: Detailed ultrasound can show the absence of the upper skull and brain, often in the first or second trimester.
• Confirmatory imaging: Additional ultrasound or other imaging confirms the diagnosis.

A diagnosis allows families to receive counseling and support and to make informed decisions with their care team.

Care and Support

There is no treatment that can reverse anencephaly. Care focuses on supporting the family.

• Counseling and support: Genetic counseling, emotional support, and clear information help families understand the diagnosis and options.
• Pregnancy and delivery planning: The care team helps families plan for the pregnancy and birth in line with their wishes and values.
• Comfort-focused care: For babies born alive, care centers on comfort and dignity.
• Bereavement support: Ongoing support is available for grieving families.

Families should not feel they caused the condition; it usually arises from factors outside their control.

Prevention

Many neural tube defects, including some cases of anencephaly, can be prevented with adequate folic acid:

• Take a daily folic acid supplement (commonly 400 micrograms) before conception and in early pregnancy; higher doses may be advised for those at increased risk
• Eat folate-rich foods, such as leafy greens, beans, and fortified grains
• Manage diabetes well before becoming pregnant
• Review medications with a doctor before pregnancy
• Discuss your history with a provider if you have had a previous affected pregnancy

When to See a Doctor

If you are planning a pregnancy or could become pregnant, talk to a doctor about folic acid and any personal risk factors, ideally before conception. During pregnancy, attend all recommended prenatal visits and screenings. Seek prompt advice if you:

• Have a personal or family history of neural tube defects
• Take medications that may affect a pregnancy
• Have diabetes or another condition that needs control before pregnancy
• Receive an abnormal screening result and need counseling and support

Related Topics

Frequently Asked Questions

References

1. Centers for Disease Control and Prevention (CDC). Facts about Anencephaly.
2. MedlinePlus, U.S. National Library of Medicine. Anencephaly.
3. March of Dimes. Neural tube defects.
4. American College of Obstetricians and Gynecologists (ACOG). Neural tube defects.