Anencephaly is a rare birth defect that occurs when the baby’s cranium bones do not form completely which prevents the cerebellum region of the brain from developing normally. The cerebellum controls advanced thinking as well as vision and other sense. This birth defect is almost always fatal for the fetus and causes stillbirth or miscarriage.

Anencephaly is classified as a neural tube birth defect. The neural tube is a part of a fetus that is supposed to close early in fetal development and form the spine and brain. When the neural tube does not close normally (by the 4th week of gestation) it can lead to major birth defects including anencephaly.

Incidence Rate for Anencephaly

Anencephaly is a very rare birth defect, occurring in only 3 out of every 10,000 pregnancies in the U.S. Anencephaly is a very serious type of birth defect that often results in death. 3 out of every 4 cases of anencephaly result in a stillbirth or babies that died within the first few days of life.

Causes of Anencephaly

The causes of anencephaly are entirely unknown. In some cases, this birth defect is believed to be connected to a chromosome or genetic abnormalities. In most cases, however, there is no evidence of any genetic predisposition.

There is some evidence that certain environmental factors may increase the potential risk of anencephaly. High temperatures during early fetal development, from either a maternal fever or a hot tub, may increase the potential risk of anencephaly. Research has also suggested that the use of certain prescription drugs during early pregnancy may have a causal connection.

The one risk factor that has been definitively linked to increased risks of anencephaly is folic acid deficiency during early pregnancy. Low folic acid levels in the mother during the early stages of pregnancy have been shown to increase the risk of neural tube defects such as anencephaly. This is why prenatal vitamins provide supplementary folic acid for pregnant or expecting mothers.

Diagnosis of Anencephaly

Anencephaly is very easy to diagnose after the baby is born based on physical abnormalities in the skull. In some cases, the sections of the skull bones may actually be missed along with the scalp.

Diagnosing anencephaly during pregnancy is much more difficult and requires a number of tests in order to be definitively diagnosed. Methods used in the prenatal diagnosis of anencephaly include:

  • Blood Testing: anencephaly can result in abnormally high levels of a particular liver protein called alpha-fetoprotein. High levels of this protein can suggest anencephaly but not definitively diagnose it.
  • Amniocentesis: testing of the amniotic fluid can be done to identify high levels of certain proteins that are associated with neural tube defects.
  • Ultrasound: abnormalities in the baby’s skull development can often be identified on ultrasound imaging. If combined with high protein levels in blood tests this can be used to make a solid diagnosis.
  • Fetal MRI Scan: a fetal MRI can be done to provide more detailed and informative imaging studies than those compared to ultrasound.

Prenatal testing for anencephaly and other neural tube defects is usually done between 14 and 18 weeks gestation.

Prognosis for Babies with Anencephaly

Anencephaly is a fatal birth defect. When this condition occurs is prevents the cerebellum area of the brain from developing enough to support life. When a fetus has this birth defect it will either result in miscarriage, stillbirth, or death within a few hours after birth. There is no method of treatment for anencephaly.

How Can Anencephaly be Prevented

The causes of anencephaly are not well understood, so there is no guaranteed way of preventing it. The most effective means of minimizing the risk of anencephaly is taking prenatal vitamin supplements before and during the early stages of pregnancy. Prenatal vitamins provide folic acid supplements for pregnant women which has been shown to greatly reduce the risk of anencephaly.

Anencephaly - Studies & Research

Bonnard, C., et al. "A loss-of-function NUAK2 mutation in humans causes anencephaly due to impaired Hippo-YAP signaling." Journal of Experimental Medicine. 217.12. (2020). (This study looked at the gene NUAK2 and its association with anencephaly. Based on their models, the researchers found that NUAK2 activity disruption caused nucleokinesis impairments and apical constrictions that lead to anencephaly. The researchers concluded that NUAK2 was “an indispensable kinase” for human brain development. They suggested the gene regulated cytoskeletal processes that regulate cell shapes in neural tube closures.)  

 Debnath, M., Sharma, D., & Mishra, S. "Prenatal diagnosis of anencephaly and acrania in pregnant females–Report series of eight cases." International Journal of Medical Science and Public Health. 9.5. (2020). (This study looked at whether evaluating fetal morphology could timely detect anencephaly and acrania. The researchers concluded that healthcare providers could use ultrasounds and alpha-fetoprotein tests to timely diagnose anencephaly and acrania in the first trimester. They concluded that a timely diagnosis could reduce both condition’s health effects. The researchers also emphasized the importance of preventing them by consuming folic acid supplements and appropriate nutrition. This study’s focus was to build awareness of anencephaly and acrania among India’s rural population.)  

 Duffy, S. "The Ultrasound Evaluation of Fetal Anencephaly." (2021). (This study looked at whether ultrasounds could accurately detect anencephaly. The researcher concluded that an ultrasound’s accuracy depended on whether the sonographers and physicians knew the right tests, appearances, and differential diagnoses to find on the test.)  

 Munteanu, O., et al. "The etiopathogenic and morphological spectrum of anencephaly: a comprehensive review of literature." Rom J Morphol Embryol. 61. (2020): 2. (This literature review looked at anencephaly’s etiology and morphology. The researchers concluded that this condition was a severe CNS malformation. They also concluded that morphological characterizations would allow for timely and accurate screenings.)  

 Wertaschnigg, D., et al. "Ultrasound Appearances of the AcraniaAnencephaly Sequence at 10 to 14 Weeks’ Gestation." Journal of Ultrasound in Medicine 39.9 (2020): 1695-1700. (This study whether ultrasounds could detect acrania-anencephaly sequences in the first trimester. Researchers used six different subtypes to determine interobserver reliability in classifying acrania-anencephaly sequence cases. The researchers found that the interobserver operator was good, with a 0.903 intraclass correlation efficient. They concluded that the use of different subtypes could detect acrania-anencephaly sequences earlier on in a pregnancy. They also concluded that timely diagnoses could result in better-managed pregnancies.)