A nuchal translucency (NT) scan is an optional ultrasound performed in the first trimester of pregnancy to help determine the babys risk of congenital conditions like Down syndrome. The scan measures the size of the clear tissue, called the nuchal translucency, at the back of the babys neck. The scan is usually done between 11 and 14 weeks of pregnancy. The fluid behind the babys neck tends to get reabsorbed by the body after 14 weeks of gestation, making it harder to measure later in pregnancy. The results of the NT scan are usually combined with findings from all of the first-trimester screenings to calculate the babys overall risk of a congenital condition. The scan is often done as part of a first-trimester screening test, and the results are used to determine if further testing is necessary. If the screening is abnormal, a diagnostic test such as chorionic villus sampling (CVS) or amniocentesis can be used to diagnose the condition. The NT scan is safe, noninvasive, and doesnt cause any harm to the mother or baby.