A nuchal translucency (NT) scan is an ultrasound scan to screen for chromosomal abnormalities such as Down syndrome in the fetus. A nuchal translucency test should be done between 11 and 13 weeks 6 days gestation. Doctors usually offer this test along with an evaluation of the nasal bones, as well as a blood test called the first trimester combined test. As with other screening tests, the nuchal translucency test does not provide any diagnosis. If you have a high risk result, your doctor will discuss whether you want to have a confirmatory test, which may be chorionic villus sampling (CVS) or amniocentesis.