What Causes Anencephaly?

Genetic and Environmental Factors May Cause This Birth Defect

pregnant woman taking folic acid tablets
There is evidence that having an adequate intake of folic acid before conception will reduce the risk of having a baby affected by any neural tube defect. Vanessa Davies/Dorling Kindersley/Getty Images

Anencephaly is a type of birth defect in which crucial parts of the baby's brain and skull fail to form. Unfortunately, babies affected by anencephaly frequently are stillborn or die at birth. Even if born alive, babies with anencephaly always die within a few days of birth. There is no treatment that can change the prognosis.

Understanding Neural Tube Defects

Anencephaly is a type of neural tube defect (NTD), which are brain, spine or spinal cord birth defects.

 These are conditions in which the developing neural tube does not close properly during the baby's development very early in the first trimester. Neural tube defects have a wide range of severity, from only minor health concerns to being 100 percent fatal. 

On the severe range of that spectrum is anencephaly, one of the most devastating diagnoses expectant parents can receive during pregnancy. Unfortunately, babies with anencephaly can never gain consciousness or carry out the physical functions of life because they are missing important parts of their brain. Because the skull is also affected by the disorder, babies with anencephaly are usually physically deformed and parts of their brain may be exposed. 

How Anencephaly Is Diagnosed

Anencephaly is often apparent on an ultrasound by the second trimester, but the first clue might be abnormalities in the alphafetoprotein blood test. Amniocentesis may be used in the diagnosis as well.

An anencephaly diagnosis is unlikely to be a false positive.

Causes of Anencephaly

Anencephaly appears to be caused by a combination of genetic and environmental factors. The interplay of these factors disrupts the closure of the neural tube, which occurs between the third and fourth week of pregnancy.

The specifics of the factors at work in anencephaly and other neural tube defects are still not well understood.

There is evidence that having an adequate intake of folic acid before conception will reduce the risk of having a baby affected by any neural tube defect, although the reasons for this are not well understood. This is why doctors advise all women of childbearing age to take folic acid supplements and eat folate-rich foods on a regular basis. Don't wait until you're already pregnant.

That said, anencephaly can occur even when moms eat a perfect diet, so it cannot necessarily be prevented and it is definitely not anyone's fault when it does occur.

The Risk of Recurrence

Parents who have a child with anencephaly may have a 4 to 10 percent risk of having a child affected by neural tube defects in a future pregnancy, although the specific neural tube defect might not be anencephaly. Doctors may advise taking high doses of folic acid before conceiving again and may recommend that the couple work with a genetic counselor as well.

Deciding What to Do After a Diagnosis

The decision of what to do after an anencephaly diagnosis can be heart wrenching.

Many parents decide to terminate the pregnancy after receiving a diagnosis of anencephaly, knowing that there is zero chance that the baby will live. Ending the pregnancy can help parents to move forward and begin the grieving process.

Other parents may have strict religious or other personal beliefs against abortion, and they may choose to carry the pregnancy to term with the full knowledge that the baby will not live more than a few days at most.

If you are facing this tragic choice, be sure to take your time and do what feels right for you and your partner. Give yourself room to grieve the loss of the baby.

It's OK to be angry, sad or to experience any other feelings. Your hospital may have grief counselors available, and there are numerous support groups available on the Internet that target couples dealing with an anencephaly diagnosis. Support groups for anencephaly tend to be geared toward a specific course of action for dealing with the pregnancy.


Anencephaly. Neurological Disorders. University of Virginia Health System. 

NINDS Anencephaly Information Page. National Institute of Neurological Disorders and Stroke.

Continue Reading