A Nuchal Translucency Screening (NT), usually performed in the first trimester as part of the First Trimester Combined Screen, evaluates the soft tissue in the back of the fetus’ neck via ultrasound. The test looks for signs of Down Syndrome and other chromosomal or genetic abnormalities by assessing the amount of fluid visible in the back of the neck. A relatively large amount of fluid in the neck is indicative of Down Syndrome or other conditions caused by the presence of extra chromosomes.
The procedure
The scan is performed with an ultrasound, and the image of the fetus’s neck and head from the side will be magnified by 75% on the screen to get an accurate measurement of the space in the back of the neck. Between 11 and 14 weeks, this area is transparent, which gives a more accurate assessment of the fluid level. If your healthcare provider sees that the measurement is large enough to be considered positive for a chromosomal abnormality, you may be tested with a more invasive procedure, like amniocentesis or chorionic villus sampling, to confirm the result. Nuchal Translucency Screening is not just offered to women with high-risk pregnancies, in fact, it is usually included in a first-trimester combined screening during one of your first healthcare provider’s appointments.
The results
Data collected from your age and blood test results, the gestational age, and the NT measurement form a statistical relationship that assesses the presence of chromosomal abnormalities. Down Syndrome can affect any pregnancy, but the chances of getting a positive result increase exponentially with your age. The measurement of the area in the back of the fetus’ neck is compared against a standard value according to gestational age. If the nasal bone is absent in the fetus at the time of the test, the chance of a chromosomal defect is high. The NT is about 75% accurate, and this detection rate increases when combined with a blood test, but your healthcare provider will likely perform a subsequent procedure to confirm a positive result.
The Nuchal Translucency Screening, in addition to other first trimester tests, is an initial indicator of potential developmental problems. A normal scan could put you at ease, knowing the risk for chromosomal defects, and a positive result will give you time to discuss further tests with your healthcare provider.
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Sources
- “Nuchal translucency test.” U.S National Library of Medicine. MedlinePlus, 6/11/2014. Web.
- “ACOG’s Screening Guidelines on Chromosomal Abnormalities.” ACOG. American College of Obstetricians and Gynecologists, 5/7/2007. Web.
