Key points
- Anencephaly (an-en-sef-ah-lee) is a serious birth defect where a baby is born without parts of the brain and skull.
- Almost all babies born with anencephaly will die shortly after birth.
- Researchers estimate that about 1 in every 5,250 babies is born with anencephaly in the United States.
What it is
Anencephaly is a fatal condition where a baby is born without parts of the brain and skull. It is a type of neural tube defect (NTD). There is no known cure or standard treatment for anencephaly.
During early pregnancy, the neural tube develops into the baby's brain and spine. The upper part helps form the baby's brain and skull, and the lower part forms the spinal cord and back bones.
In anencephaly, the upper part of the neural tube does not close all the way. The baby is often born without the front part of the brain (forebrain) and the thinking and coordinating part of the brain (cerebrum). The remaining parts of the brain are often not covered by bone or skin.
Risk factors
Not all causes of anencephaly are known, but certain factors can affect the risk of a baby having anencephaly. This can include a change in the baby’s genes or a combination of genes and other factors.
Researchers have identified factors in pregnant people that might increase the risk for anencephaly:
- Low folate (vitamin B9) levels during early pregnancy1
- Pre-existing health conditions, such as diabetes, that are not well controlled
- Certain medications, such as antiseizure medications
- Overheating (like getting in a hot tub) or fever
Importance of Folic Acid
Screening and diagnosis
Anencephaly can be diagnosed during pregnancy or after the baby is born.
During pregnancy
During pregnancy, there are screening tests to check for birth defects and other conditions. Being pregnant with a baby with anencephaly can result in an abnormal result on a blood or serum screening test. Anencephaly can also be seen during an ultrasound exam.
After the baby is born
In some cases, anencephaly might not be diagnosed until after the baby is born. Anencephaly is immediately seen at birth.
Expected outcomes
There is no known cure or standard treatment for anencephaly. Pregnancy loss is high. Almost all babies born with anencephaly will die shortly after birth.
- Crider KS, Qi YP, Yeung LF, Mai CT, Head Zauche L, Wang A, Daniels K, Williams JL. Folic Acid and the Prevention of Birth Defects: 30 Years of Opportunity and Controversies. Annu Rev Nutr. 2022 Aug 22;42:423-452.
- Stallings, E. B., Isenburg, J. L., Rutkowski, R. E., Kirby, R. S., Nembhard, W.N., Sandidge, T., Villavicencio, S., Nguyen, H. H., McMahon, D. M., Nestoridi, E., Pabst, L. J., for the National Birth Defects Prevention Network. National population-based estimates for major birth defects, 2016–2020. Birth Defects Research. 2024 Jan;116(1), e2301.