Nuchal Translucency Test
Nuchal translucency screening, or NT screening, is an ultrasound test. It screens for Down syndrome and other disorders that are caused by chromosomal abnormalities, as well as congenital heart defects.
Nuchal translucency is a collection of fluid under the skin at the back of a baby’s neck. The nuchal translucency scan measures the thickness of this fluid to assess the risk of Down’s syndrome. If the scan reveals more fluid than usual, it could be a sign of Down’s syndrome. A nuchal translucency scan can only indicate the level of risk of your baby having Down’s syndrome. To get a definitive diagnosis, a test such as CVS or amniocentesis is necessary. These tests also carry a small risk of miscarriage though so your doctor will only suggest them if there is a high risk of Down’s.
The nuchal translucency scan is usually advised in first-time pregnancies, high-risk pregnancies and in pregnant women who are over 35 years of age. The NT scan is usually performed between 11 and 14 weeks of pregnancy. Before 11 weeks the scan is technically difficult because the baby is so tiny and, after 14 weeks, excess fluid may be absorbed by the baby’s developing lymphatic system. A large research study involving over 100,000 pregnancies found that about 75 percent of babies with Down’s syndrome were correctly identified using this method. When combined with a blood test, the detection rate improves to about 90 percent. However, to achieve these detection rates, it is important that the NT is measured accurately. This is why the scan should only be done by a trained professional