Facts about Anencephaly
Anencephaly (pronounced an-en-sef-uh-lee) is a serious birth defect in which a baby is born without parts of the brain and skull.
What is anencephaly?
Anencephaly is a serious birth defect in which a baby is born without parts of the brain and skull. It is a type of neural tube defect (NTD). As the neural tube forms and closes, it helps form the baby’s brain and skull (upper part of the neural tube), spinal cord, and back bones (lower part of the neural tube).
Anencephaly happens if the upper part of the neural tube does not close all the way. This often results in a baby being 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.
CDC estimates that each year, about 3 pregnancies in every 10,000 in the United States will have anencephaly.1 This means about 1,206 pregnancies are affected by these conditions each year in the United States.
Causes and Risk Factors
The causes of anencephaly among most infants are unknown. Some babies have anencephaly because of a change in their genes or chromosomes. Anencephaly might also be caused by a combination of genes and other factors, such as the things the mother comes in contact with in the environment or what the mother eats or drinks, or certain medicines she uses during pregnancy.
Like many families of children with a birth defect, CDC wants to find out what causes them. Understanding the factors that are more common among babies with a birth defect will help us learn more about the causes. CDC funds the Centers for Birth Defects Research and Prevention, which collaborate on large studies such as the National Birth Defects Prevention Study (NBDPS; births 1997-2011), to understand the causes of and risks for birth defects, including anencephaly.
CDC researchers have reported important findings about some factors that affect the risk for anencephaly:
- Low intake of folic acid before getting pregnant and in early pregnancy increases the risk of having a pregnancy affected by neural tube defects, including anencephaly.2
- Since the United States began fortifying grains with folic acid, there has been a 28% decline in pregnancies affected by neural tube defects (spina bifida and anencephaly).1
- Babies born to Hispanic mothers are at an increased risk for anencephaly. Reasons for the increased risk among Hispanic mothers are not well understood.3
CDC continues to study birth defects, such as anencephaly, and how to prevent them. If you are pregnant or thinking about becoming pregnant, talk with your doctor about ways to increase your chances of having a healthy baby.
Anencephaly can be diagnosed during pregnancy or after the baby is born.
During pregnancy, there are screening tests (prenatal tests) to check for birth defects and other conditions. Anencephaly would result in an abnormal result on a blood or serum screening test or it might be seen during an ultrasound (which creates pictures of the body). For more information about screening and confirmatory tests during pregnancy, visit CDC’s birth defects diagnosis web page.
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.
There is no known cure or standard treatment for anencephaly. Almost all babies born with anencephaly will die shortly after birth.
- CDC. Updated Estimates of Neural Tube Defects Prevented by Mandatory Folic Acid Fortification — United States, 1995–2011. MMWR Morb Mort Wkly Rep. 2015: 64(01); 1-5.
- CDC. Spina Bifida and Anencephaly Before and After Folic Acid Mandate --- United States, 1995--1996 and 1999—2000. MMWR. May 7, 2004 / 53(17);362-365.
- Canfield MA, Mai CT, Wang Y, O’Halloran A, Marengo LK, Olney RS, et al. The Association Between Race/Ethnicity and Major Birth Defects in the United States, 1999–2007. Am J Public Health. 2014;104(9):e14-e23.
- Page last reviewed: November 9, 2015
- Page last updated: November 9, 2015
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