Anencephaly Fast Facts

Anencephaly is a condition where the tissue that forms an embryo’s brain and spinal cord doesn’t develop correctly. The problem occurs before birth and is usually fatal before or shortly after birth.

Anencephaly is a type of condition called a neural tube defect (NTD). Other NTDs include spina bifida and iniencephaly.

Anencephaly affects female babies more often than males.

Anencephaly affects about 1 in every 5,000 babies in the United States.

United Brain Association

Anencephaly affects about 1 in every 5,000 babies in the United States.

What is Anencephaly?

Anencephaly is a defect of the central nervous system that develops before birth. The condition arises when an embryo’s neural tube, the tissue that eventually forms the central nervous system, develops incorrectly. As a result, the neural tube doesn’t close as it normally does in the first few weeks of pregnancy, resulting in an abnormally formed brain, skull, and spinal cord.

The condition is almost always fatal to the baby before or soon after birth, typically within a few hours. In most cases, a baby with anencephaly will miscarry or be stillborn. Those who survive birth usually die within a few hours.

Features of Anencephaly

Anencephaly results in severe malformations of the baby’s brain and skull, including:

  • Absent or underdeveloped cerebrum, the large part of the brain that controls major functions such as thought, speech, and voluntary movement
  • Absence of bone covering the brain
  • Lack of skin covering the brain and skull

What Causes Anencephaly?

Anencephaly occurs when the neural tube, a group of cells that becomes the central nervous system during early fetal development, does not form properly during pregnancy. The abnormal development results in nervous systems malformations called neural tube defects. In the case of anencephaly, the upper part of the neural tube does not close as it should, and the brain and skull develop incompletely.

Scientists are not sure what causes anencephaly. Genetics, environment, and nutrition of the mother during pregnancy all seem to play a role in developing anencephaly, spina bifida, and other neural tube defects. Still, the interplay of all these factors is not well understood.

Research has indicated several risk factors that appear to increase the chance of neural tube defects:

  • Folate deficiency. When a mother has a nutritional deficiency of folate (also called vitamin B-9 or folic acid) during pregnancy, her baby’s risk of anencephaly or other neural tube defects increases.
  • Family history. Risk increases in families in which previous children have had anencephaly or other neural tube defects. Risk is also higher when the mother herself has suffered from a neural tube defect. Most cases of anencephaly, however, occur in babies with no family history of the disorder.
  • Obesity and Diabetes. Women who are significantly overweight or have uncontrolled high blood sugar are at higher risk of having a baby with anencephaly.
  • Exposure to high temperatures. The risk of anencephaly seems to increase if an embryo is exposed to high temperatures during pregnancy. For example, this can occur if the mother has a high fever or uses a sauna or hot tub.
  • Drug reactions. Certain anti-seizure medications, such as phenytoin, carbamazepine, and valproic acid, seem to interfere with the body’s folate processing and increase the risk of neural tube defects when taken by the mother during pregnancy. In addition, the use of some diuretics, antihistamines, and sulfa drugs during pregnancy can also increase risk.
  • Substance abuse. The use of opioids such as heroin or hydrocodone early in pregnancy increases the risk of neural tube defects.

Is Anencephaly Hereditary?

The role that inherited factors play in the risk of neural tube defects is unclear. Most cases occur in babies with no family history of the conditions. However, the fact that risk increases with a family history of neural tube defects suggests that genetics play some role. Genetic factors are also indicated by the fact the disorder is more common in females than in males.

How Is Anencephaly Detected?

Anencephaly may be detected before birth via ultrasound imaging exams, magnetic resonance imaging (MRI), blood tests, or amniocentesis. In cases where anencephaly is not detected during pregnancy, the malformations characteristic of the disorder are visible at birth.

How Is Anencephaly Diagnosed?

The diagnostic process for anencephaly typically involves imaging scans, blood tests, and other screening procedures during pregnancy. Exams and tests used to identify anencephaly include:

  • Blood tests. A test called a quad marker screen measures levels of a chemical called alpha-fetoprotein (AFP) in the baby’s blood. AFP levels are often elevated in the case of anencephaly.
  • Imaging scans. Ultrasound or MRI scans of the baby can often detect anencephaly during pregnancy.
  • Amniocentesis. Examination of the amniotic fluid that surrounds the baby in the womb measures levels of AFP and another chemical called acetylcholinesterase, either of which may be elevated in the case of anencephaly.


How Is Anencephaly Treated?

There is no treatment for anencephaly.

How Does Anencephaly Progress?

Anencephaly is always fatal to the baby. In most cases, the baby miscarries or is stillborn. When the baby survives birth, the condition is usually fatal within a few hours or days.

How Is Anencephaly Prevented?

Because anencephaly has no treatment, the most effective way to deal with the condition is to take steps to prevent it. Women who are pregnant or could become pregnant can reduce their risk of having a baby with iniencephaly or other neural tube defects by proactively addressing several risk factors.

  • Ensure an adequate intake of folic acid. The recommended daily dose of folic acid is 400 micrograms (mcg). Women who have had a previous pregnancy with a neural tube defect may be encouraged to take a higher dose. Consult a doctor for guidance.
  • Manage diabetes according to your doctor’s instructions, and have blood sugar levels under control before you become pregnant.
  • Take steps to control obesity.
  • Avoid hot tubs, saunas, and high-temperature environments during pregnancy. Treat high fevers promptly with the over-the-counter fever reducer acetaminophen.
  • Tell your doctor about any medications or dietary supplements you’re taking.

Anencephaly Caregiver Tips

  • Take time to process your grief after a diagnosis of anencephaly. Everyone grieves in their own way, and you shouldn’t hold yourself to anyone else’s standards or schedules. Acknowledge the pain you feel, and don’t be afraid to seek help when you need it.
  • Find a community. Online support groups can be a valuable source of information and emotional assistance.

Anencephaly Brain Science

Anencephaly occurs when the upper portion of the fetus’s neural tube fails to close normally in the third or fourth week after fertilization. The malformation of the neural tube causes the brain to develop abnormally. Typically, the cerebral hemispheres and cerebellum do not fully develop, impairing most voluntary brain functions. In most cases, the skull and scalp are underdeveloped as well, leaving the brain exposed.

Much of the research regarding neural tube defects is focused on understanding the genetic component of the disorders. Of particular interest are genes that play a role in the processing of folic acid. A deficiency of the chemical seems to play a vital role in the development of neural tube defects. The most studied of these genes is the MTHFR gene, but several other genes are also associated with folic acid. So far, no consistent link between variations in any of these genes and anencephaly has been found.

Anencephaly Research

Title: Folate Metabolism in Normal Weight and Obese Women of Child-bearing Age

Stage: Completed

Contact: Lynn B Bailey, PhD

University of Georgia

Athens, GA 

Current recommendations established in 1998 specify that all women capable of becoming pregnant consume 400 micrograms of folate daily from supplements, fortified foods, or both, in addition to consuming food folate from a varied diet. Despite this recommendation, obese women have a lower folate status than women of normal weight, which suggests that obesity may have a negative impact on folate metabolism. Therefore, the objective of this study is to determine if there are differences in the metabolic response to a single dose of folate between normal weight and obese women of childbearing age. The two groups of women will be given the currently recommended amount of folic acid, 400 micrograms, and blood samples will be taken before the vitamin is given and at various points afterward to determine serum folate response to the folate dose. Results of this research should help determine if folate requirements are higher for obese than for non-obese women. The long-term goal of this and follow-up studies is to generate data that will contribute to the evidence base used by scientific advisory panels to determine whether dietary folate intake recommendations should be based on body weight.


Title: Genetics of Spina Bifida and Anencephaly

Stage: Completed

Contact:  Allison Ashley-Koch, PhD

Duke University

Durham, NC 

This research study aims to discover the genetic and environmental factors that contribute to the cause of neural tube defects such as spina bifida and anencephaly. Ultimately, this type of research may result in improved diagnosis, improved treatment, and possibly prevention.  


Title: Dosage Effects of Folic Acid on Blood Folates of Honduran Women

Stage: Completed

Contact:  Gayle Milla

Project Healthy Children

San Pedro Sula, Honduras 

CDC staff at the National Center on Birth Defects and Developmental Disabilities have been working closely with a Honduras-based organization, Project Healthy Children (PNS) and the Ministry of Health, on a folic acid supplementation study among female maquila workers. Participants are divided into two groups. One group receives a 1.0-milligram dose daily, while the other group receives a 5.0-milligram dose weekly. This study aims to assess serum blood folate levels measured at baseline, midpoint, and endpoint. Hypothesis: Folic acid (5mg) given once weekly is as effective as folic acid (1mg) given daily in raising blood folate levels.

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