Facts about 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). These are birth defects that happen during the first month of pregnancy, usually before a woman knows she is pregnant. 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.
Almost all babies born with anencephaly will die shortly after birth. CDC estimates that each year, about 1 in every 4,859 babies in the United States will be born with anencephaly.1
Women can take steps before and during pregnancy to reduce the risk of having a baby born with birth defects. Such steps include taking a daily multivitamin with folic acid (400 micrograms), not smoking, and not drinking alcohol during pregnancy.
Learn more about how to prevent birth defects »
Causes and Risk Factors
Like many families affected by birth defects, CDC wants to find out what causes them. Research gives us important clues about things that might raise or lower the risk of having a baby affected by birth defects, such as anencephaly. Those clues help us develop sound public health policies for prevention.
CDC works with many other researchers to study risk factors that can increase the chance of having a baby affected by anencephaly. Scientists believe that many factors such as genes, behaviors, and things in the environment are involved. 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
- There has been a 27% decline in pregnancies affected by nueral tube defects (spina bifida and anencephaly) since the United States began fortifying grains with folic acid.2
- Babies born to Hispanic mothers are at an increased risk for anencephaly.3 Reasons for the increased risk among Hispanic mothers are not well understood.
CDC continues to study birth defects like anencephaly and how to prevent them. If you are pregnant or thinking about becoming pregnant, talk with your doctor about ways to increase your chance 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).
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.
- Parker SE, Mai CT, Canfield MA, Rickard R, Wang Y, Meyer RE, et al; for the National Birth Defects Prevention Network. Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol. 2010;88(12):1008-16.
- 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.
- Williams LJ, Rasmussen SA, Flores A, Kirby RS, Edmonds LD. Decline in the prevalence of spina bifida and anencephaly by race/ethnicity: 1995-2002. Pediatrics. 2005;116(3):580–6.
- Page last reviewed: October 21, 2014
- Page last updated: October 21, 2014
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