Anencephaly

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. Anencephaly is almost always fatal for the fetus and causes stillbirth or miscarriage.

This defect is classified as a neural tube birth defect because it is caused by the failure of the anterior neural tube to close. 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.

The closure - called a rostral closure - normally occurs early in brain development. The closure of the posterior neural tube occurs after the brain is more developed. This has much less significant consequences that are correctable by surgery. But the failure of the posterior neural tube to close can also cause very serious complications such as such as paraplegia and difficulty with bladder and bowel functions.

Anencephaly is a fatal condition because of the severe brain malformation that is present. A child with this defect is expect to live at most one month, although there is a case report of a child who lived for 28 months. It is very painful for the parents who often endure enormous grief over the loss of their child.

Incidence Rate for Anencephaly

Anencephaly is a 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.

What 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.

When Is Anencephaly Diagnosed?

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

Anencephaly is 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 be missed along with the scalp.

Diagnosing anencephaly during pregnancy is much more difficult and requires testing 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.
What Is the 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 shortly after birth. There is no method of treatment for anencephaly.

Most anencephalic fetuses die shortly after childbirth because they lack essential brain functions. Only 32% of anencephalic fetuses carried to term can be characterized as live births.

Intense efforts can prolong life. With intensive neonatal care, including intubation and usually assistance with respiration, some anencephalic fetuses can survive for seven days to two months and sometimes longer. Without intensive care, only % of liveborn anencephalic babies survive to seven days.

How Can Anencephaly be Prevented?

The causes of anencephaly are not well understood, so there is no guaranteed way of preventing it. One thing seems crystal clear: it is not the mother's fault.

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 - and even before you conceive - that reduces the risk of anencephaly.

For some unknown reason, maternal age between ages 26-30 causes a greater risk of anencephaly.

One study found that pregnant women with the common cold in the first trimester had a four to five times greater risk of anencephaly.

Finally, it is worth noting that some believe that SSRIs - Paxil, Zoloft, Prozac, etc, - cause an increased risk of adverse pregnancy outcomes, including anencephaly.

Can I Continue a Pregnancy with Anencephaly?

This is a difficult issue. Continuation of pregnancy after a diagnosis of anencephaly is thought by some to be medically safe. Other doctors may say it is in the mother's best interest, both physically and medically, to terminate her pregnancy once the diagnosis of anencephaly was made. There are many emotional and religious implications for many.

Obviously, you want to consult with your doctor and make the best decision.

Anencephaly - Studies and 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. 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 Acrania-Anencephaly 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.)