Anencephaly: causes, risks & what you can do

About 1,206 pregnancies are affected by anencephaly each year in the U.S.

Anencephaly is a serious birth defect in which a baby is born without parts of the brain, skull and scalp. As a baby’s neural tube develops and closes, it helps form the baby’s brain and skull, spinal cord, and back bones. Anencephaly is a type of neural tube defect (NTD) that happens if the upper part of the neural tube does not close all the way. A baby with anencephaly will be missing large parts of the brain that are necessary for thinking, hearing, vision, emotion and coordinating movement. Other parts of the brain are often not covered by bone or skin.

Babies born with anencephaly have reflexes such as breathing and response to touch and sound, however because of the severity of the condition, almost all babies with anencephaly die before birth or within a few hours or days after birth.

What causes anencephaly?

In most cases, the cause is unknown. Some cases are caused by a change in the baby’s genes or chromosomes. Anencephaly may also be caused by a combination of genes and other environmental factors. Scientists are continuing to study anencephaly in order to discover the causes.

What are the risk factors?

  • Low intake of folic acid before getting pregnant and in early pregnancy increases the risk of having a pregnancy affected by a NTD including anencephaly.
  • Babies born to Hispanic mothers are at an increased risk for anencephaly; reasons for the increased risk are not well understood.

How is anencephaly diagnosed?

  • During pregnancy: a woman can have screening tests done during her prenatal visits. Anencephaly would result in an abnormal result on a blood or serum screening test. Anencephaly might be seen during an ultrasound.
  • After a baby is born: anencephaly is immediately seen at birth.

Is there anything you can do to lower your risk?


  • Take a multivitamin with at least 400 micrograms of folic acid every day before and early in pregnancy. Make sure to take your multivitamin even if you are not thinking about becoming pregnant any time soon. Since the U.S. started requiring that folic acid be added to certain foods, there has been a 28% reduction in cases of babies born with NTDs.
  • If you are pregnant, make sure you go to all of your prenatal visits and eat a well-balanced diet
  • Avoid alcohol and smoking and talk to your provider about any medications or drugs you are taking.

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