Nuchal Translucency

What is nuchal translucency?

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

What does nuchal translucency test for?

A nuchal translucency scan looks at the space at the back of the fetus's neck called the nuchal fold. All fetuses have fluid behind their necks. Healthcare providers have found that more fluid tends to build up at the base of a fetus's neck when it has chromosomal or genetic conditions. More fluid in this area could indicate the fetus has a condition like Down syndrome (trisomy 21), Patau syndrome (trisomy 13) or Edwards syndrome (trisomy 18). A higher NT measurement may also indicate an increased risk for congenital heart conditions. The results of the NT scan can determine if the fetus is likely or unlikely to have these conditions. At the time of nuchal translucency, the ultrasound also screens for some basic anatomical structures in the developing fetus. Other anomalies identified at the time of NT may increase the risk for genetic or structural conditions.

When is a nuchal translucency scan done?

Your healthcare provider performs an NT scan when between 11 and 13 weeks of gestation or when the fetus is between 45 millimeters and 84 millimeters from crown (top of their head) to rump (bottom of their torso). This is because the fluid behind its neck tends to get reabsorbed by its body after 14 weeks of gestation. This makes it harder to measure later in pregnancy. NT tests are often done as part of a first-trimester screening test.

What is a first-trimester screening test?

A first-trimester screening (or combined sequential screening) determines the risk of congenital conditions. In addition to the NT scan, a first-trimester screening uses blood tests to help determine if the fetus is at risk for congenital conditions. Combining a blood test and the NT scan is more accurate than the NT scan alone.

Who should get a nuchal translucency screening?

Anyone can get a nuchal translucency screening as long as they’re between 11 and 13 weeks of pregnancy. The ultrasound is optional for all people who are pregnant. Talk to your healthcare provider to make sure you understand what each test is looking for.

How is nuchal translucency screening done?

Your healthcare provider uses abdominal ultrasound (or sometimes, a vaginal ultrasound) for a nuchal translucency test. First, they’ll spread ultrasound gel on your stomach. Then, they’ll move a transducer (a handheld wand) over your stomach. Images of the fetus will appear on a screen. Measurements will be taken of the fluid-filled space behind the fetus’s neck. The fluid area is measured in millimeters.

How are the results of a nuchal translucency test calculated?

The results of your NT scan aren’t usually calculated alone. Your healthcare provider will typically combine findings from all of your first trimester screenings to calculate the fetus's overall risk of a congenital condition. In most cases, you’ll be offered a blood test along with the NT scan to improve the accuracy of the screening. Your age and the fetus's nasal bone can also be factors if blood tests aren’t done.

Your healthcare provider will share your results from the NT scan with the first-trimester or sequential screening as a mathematical risk. A normal amount of fluid means the chances of a congenital condition are lower. An increased amount of fluid means there’s a higher chance that a congenital or genetic condition is present. For example, your result may indicate a 1 in 300 chance. This means that for every 300 fetuses with the fluid measurement, only one of them had a congenital condition.

It’s important to note that your healthcare provider won’t diagnose a condition based on the NT scan. NT scans are screenings and are only done to determine the likelihood of having a condition. If the NT is increased, your doctor or genetic counselor will discuss additional testing options, including chorionic villus sampling (CVS). Many times, an increased NT isn’t related to a chromosomal or genetic condition, so additional testing is always recommended.

How accurate is the nuchal translucency test?

NT screenings alone can detect about 70% of trisomy 21, or Down syndrome cases. Many healthcare providers combine a normal NT ultrasound with blood screenings. The accuracy of predicting conditions increases to about 95% when combined with first-trimester blood tests.

Are there any risks to the screening?

No, nuchal translucency is a low-risk screening.

What does an abnormal nuchal translucency test mean?

NT screenings only show the risk of the fetus having a condition. If your screening is abnormal, your healthcare provider can use a test like chorionic villus sampling (CVS) or amniocentesis (later in pregnancy) to diagnose the condition.

CVS is when tissue is taken from your placenta and tested for genetic conditions. Amniocentesis is when a needle is used to draw amniotic fluid from your uterus. This fluid contains cells that contain genetic information to diagnose abnormalities or infectious conditions.

Your healthcare provider may also want to take a closer look at the fetal heart with a fetal echocardiogram. An abnormal NT scan is also associated with fetal heart defects.

Try not to panic. Just because your results are irregular doesn’t mean the fetus has a problem. Your healthcare provider will run further tests or look for other indications of a problem on your ultrasound or in your bloodwork. They may refer you to a genetic counselor to better understand the conditions and the risks associated with them.

What is normal nuchal translucency measurement?

The amount of fluid in your fetus's neck increases with gestational age. Different organizations have slightly different cutoffs at which they’ll recommend additional testing. These are based on the NT, as well as gestational age. For most pregnancies, NT above 3 millimeters prompts a discussion of genetic counseling and additional testing.

Does an abnormal nuchal translucency scan mean my baby has Down syndrome?

No, an abnormal nuchal translucency scan doesn’t mean the fetus has Down syndrome or any other congenital syndrome. It might mean the fetus is at a higher risk or has a greater chance of having these conditions. If the NT is normal, healthcare providers prefer to use a blood test in addition to the NT scan because it’s a more accurate assessment of your chances. In some cases, more prenatal testing is needed to determine the fetus's chances of being born with a genetic condition.

How long does it take to get results?

Most healthcare providers can interpret the NT ultrasound on the same day. Blood work collected from the first-trimester screening will take at least a few days or weeks to return. Most healthcare providers will wait until they have all results to calculate if the fetus is at risk.

A note from Cleveland Clinic

A nuchal translucency (NT) scan can help determine how likely it is that the fetus has a congenital or genetic condition. If you have an irregular result, don’t panic. NT tests are screenings, and abnormal tests mean more tests are needed. There’s still a chance that you’ll have a healthy baby. Talk to your healthcare provider about what your test results mean and what they recommend next. It might also help to talk through your options with a genetic counselor and discuss the risks and benefits of further testing.