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Anencephaly is part of the spectrum of neural tube defects wherein the neural tube, a narrow channel that is supposed to fold and close by the third and fourth weeks of pregnancy to form the brain and spinal cord, fails to do so.  This results in the absence of the brain (particularly the cerebral hemispheres and the cerebellum) and the skull.  Occasionally, the open cranial vault is covered by skin.  Anencephaly results in fetal loss, stillbirth, or neonatal death.


There are multiple factors involved in the transmission of this condition, with an interplay of environmental factors and several genes.  Although the exact genes causing anencephaly still have not been pinpointed, genes that are involved with folate metabolism have been implicated.  Examples are the metylenetratrahydrofolate reductase (MTHFR) and VANGL1, which have been associated with an increased risk of occurrence of neural tube defects. 

Studies have shown that supplementation with folic acid among women of childbearing age may have a preventive effect.  Anticonvulsant medications such as valproic acid, is notorious for causing spina bifida, another kind of neural tube defect.  Exposure to such medications may also increase the chance of anencephaly occurring.  Hyperthermia, or increased body temperature of the mother, has also been considered as a risk factor for the development of anencephaly.  Examples are staying in bath tubs or maternal fever during early pregnancy.


Birth prevalence of anencephaly is approximately 1.2 per 10,000 births, however, prevalence during pregnancy is higher at approximately 1 per 1,000 pregnancies.  The exact number is not known because most of these pregnancies result in miscarriage.  Females are more frequently affected than males. 

Clinical Presentation

Anencephaly is easily diagnosed at birth because of the absence of the skull and significant portion of the brain.  Skin may cover the lesion occasionally, and facial features may appear abnormal.  The affected infant is usually deaf, blind, unconscious, and unable to sense pain. 


Ultrasonography during pregnancy confirms the diagnosis of anencephaly.  This can be done after the twelfth week of pregnancy, when ossification of the skull normally occurs.  In the first trimester, seen would be an absent skull, decreased length of the infant from the crown to the rump, exencephaly or exposed neural tissue with a lobular appearance, the absence of the normal contour of the head.  In the latter part of the pregnancy, polyhydramnios, or excess amount of amniotic fluid is noted because of the fetus’ inability to swallow the amniotic fluid. Amniocentesis may be performed to detect increased levels of alpha-fetoprotein during the latter part of the first trimester and second trimester.  Maternal serum alpha-fetoprotein (MSAFP) can also be obtained during the second trimester. 


There is no cure for anencephaly.  In most cases, supportive measures are offered.  Hydration, nutrition, and comfort measures are given.  Aggressive measures such as surgery, artificial ventilation, and medications are considered futile.


Prognosis for affected infant is extremely poor, as such condition is not compatible with life.  If the infant is not stillborn, death may occur within a few hours or days following birth. 


Folic acid supplementation has been proven to reduce the risk of anencephaly and other neural tube defects by approximately two thirds.  Women who are planning to get pregnant or pregnant women are recommended to consume 0.4mg of folic acid daily.

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