Nuchal (pronounced “NEW-kuhl”) translucency (NT) is an ultrasound that measures the amount of fluid behind your baby’s neck in the first trimester of pregnancy. A small amount of fluid is normal, and measuring the amount of fluid can help calculate your baby’s chances of having a chromosomal or genetic variant. NT ultrasound is a screening test — it doesn’t diagnose a condition. It helps your healthcare provider determine if your baby is at risk and if further tests should be recommended.

The results of the NT scan can determine if your baby is likely or unlikely to have these conditions. At the time of nuchal translucency, the ultrasound also screens for some basic anatomical structures of your unborn baby (fetus).

Doctor performs an NT scan when your baby is between 11 and 13 weeks of gestation or when your baby is between 45 millimeters and 84 millimeters from their crown (top of their head) to rump (bottom of their torso). This is because the fluid behind your baby’s neck tends to get reabsorbed by the body after 14 weeks of gestation. This makes it harder to measure later in pregnancy.