What Is Nuchal Translucency Screening?
A nuchal translucency scan is two-part test performed during the 11th to 13th week of pregnancy. The screening is done by blood test along with a nuchal fold scan and can determine if a baby is at high risk for chromosomal abnormalities such as Down syndrome.
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Significance
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A blood test is done to measure human chorionic gonadotropin as well as pregnancy-associated plasma protein A, according to the New England Journal of Medicine (NEJM). Results that come back with abnormally high or low hCG and protein A may indicate a problem.
Function
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Once the blood test is complete, an abdominal ultrasound is done. The NTS ultrasound measures the fluid that collects under the fetus's skin in the neck region. "Mathematical modeling has suggested that combining the measurement of biochemical analytes and nuchal translucency during the first trimester may identify up to 89 percent of cases of Down's syndrome,"notes the NEJM study.
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Types
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In addition to Down syndrome or trisomy 21, the tests can also detect trisomy 18. Trisomy 18 is caused by an extra chromosome; very few babies with trisomy 18 survive to birth, according to Dartmouth-Hitchcock Medical Center.
Facts
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The NTS is routinely performed on pregnant women over the age of 35 because they are at a higher risk of having a baby with chromosomal abnormalities. However, pregnant women under the age of 35 can request the test from their practitioner.
Warning
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Approximately 5 percent of normal pregnancies may receive a false positive result. "A positive test means that you have a 1/100 to 1/300 chance of experiencing one of the abnormalities," according to American Pregnancy.
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