An Overview of Anencephaly and Its Prevalence in Newborns

Anencephaly is a serious birth defect that affects the development of an infant's brain, skull, and scalp. The prevalence of anencephaly can vary by region and its effects are often fatal, with no treatment or cure available in most cases. Learn more about this condition and its symptoms here.

What is Anencephaly?

Anencephaly is a serious birth defect usually diagnosed prenatally, during which an infant is born without the major portion of their brain, skull, and scalp. Due to the absence of these components, infants with anencephaly may be eyeless and deaf, though they are still typically able to move their arms or legs. Those born with the condition usually die within several hours or days after birth.

What Causes Anencephaly?

The exact cause of anencephaly is unknown; however, it can be linked to genetic or environmental factors, or a combination of both. Genetic conditions associated with anencephaly include trisomy 13, trisomy 18 and triploidy. Additionally, maternal exposure to certain substances, like the pesticide polychlorinated biphenyls (PCBs), during pregnancy may increase the risk of anencephaly and other birth defects.

Are There Risk Factors?

There are a number of factors that increase the risk of anencephaly, such as maternal age. Women age 35 and older who become pregnant have a higher risk of having a baby with anencephaly. Additionally, women who have had previous pregnancies affected by neural tube defects, including anencephaly, may be at increased risk. Lastly, certain genetic conditions may also put a person at greater risk for anencephaly in the developing fetus.

How Common is Anencephaly?

Anencephaly is among the most serious types of neural tube defects, it is also more common in certain ethnic and racial groups. While anencephaly itself is rare, more than one-third of neural tube birth defects are estimated to be fatal. Diagnosis can often be made prenatally with an ultrasound exam; however, some cases of anencephaly may not be detected until after birth.

How Is Anencephaly Diagnosed?

Anencephaly can be diagnosed prenatally by ultrasound or magnetic resonance imaging (MRI). An ultrasound can detect an enlargement of the anterior fontanelle, absence of one or both kidneys, as well as an abnormal shape to the head. Evidence of fluid buildup in the brain—hydrocephalus—may also be seen on ultrasound, however not all cases of anencephaly have associated hydrocephalus. MRI may be used for a more detailed assessment for those cases where ultrasound findings are inconclusive. Postnatal diagnosis is usually made shortly after birth though clinical examination and confirmatory imaging studies.

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