Nuchal Translucency

Nuchal (“NEW-kuhl”) translucency (NT) is a type of prenatal 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. More fluid tends to build up at the base of a fetus’s neck when it has a chromosomal or genetic condition. During the scan, your provider also checks early physical features, like its nasal bone.

NT ultrasound is a screening test — it just estimates risk. If your provider sees anything irregular, they’ll recommend more tests. Anyone between 11 and 13 weeks pregnant can choose to have an NT screening. Talk to your provider to make sure you understand what the test is for and what the results tell you.

What does nuchal translucency look for?

The screening looks at fluid buildup behind your child’s neck. More fluid could mean they have a higher risk of:

• Down syndrome (trisomy 21)
• Patau syndrome (trisomy 13)
• Edwards syndrome (trisomy 18)
• Congenital heart conditions

What week is a scan done?

Your healthcare provider performs an NT scan between 11 and 13 weeks. This is when the fetus is between 45 millimeters (mm) and 84 millimeters from crown (top of their head) to rump (bottom of their torso). This is because the fluid gets reabsorbed after 14 weeks. It makes it harder to measure at that point.

How is nuchal translucency screening done?

Your healthcare provider performs an abdominal ultrasound. (Sometimes, they’ll perform a vaginal ultrasound instead.) They spread gel on your stomach and move a handheld wand across it. The wand sends images of the fetus to a screen. This is where your provider measures the fluid-filled space behind its neck. The fluid area is measured in millimeters.

How are the results calculated?

The results of your NT scan aren’t usually calculated alone. Your healthcare provider will typically combine findings from all your first-trimester screenings to calculate your child’s risk of a congenital condition. Looking at several tests improves the accuracy of the screening.

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 condition is present. For example, your result may show a 1 in 300 chance. This means that for every 300 fetuses with that fluid measurement, only one of them had a congenital condition.

It’s important to note that your provider won’t diagnose anything based on the results of an NT scan. NT scans are screenings. They only tell you the likelihood of your child having a condition. Your provider uses your results to determine whether further testing is necessary.

How accurate is the test?

NT screenings alone can detect about 70% of Down syndrome cases. Many healthcare providers combine results of an NT ultrasound with blood screenings. The accuracy of predicting conditions increases to about 95% when combined with noninvasive prenatal testing (NIPT).

Are there any risks to the screening?

No, nuchal translucency is a low-risk screening. It only uses ultrasound.

Can NT show if it’s a boy or girl?

No. This screening isn’t used for finding out your baby’s sex.

How long does it take to get results?

Most healthcare providers can read 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 providers will wait until they have all the results to calculate whether the fetus is at risk.

What is a normal nuchal translucency measurement at 12 weeks?

If the NT measurement is higher than 3 mm at 12 weeks, your provider will usually talk with you about doing more testing.

What happens if the results are abnormal?

NT screenings only show the risk of the fetus having a condition. If your screening is abnormal, your healthcare provider can use other tests to diagnose the condition. These include chorionic villus sampling (CVS) or amniocentesis. Your provider may also want to take a closer look at your child’s heart with a fetal echocardiogram.

Try not to panic. Just because your results are irregular doesn’t mean there’s a problem. Your provider will run further tests. Or they’ll look for other signs of a problem on your ultrasound or in your bloodwork. They may refer you to a genetic counselor. A genetic counselor can help you better understand the conditions your child may have.

Does an abnormal scan mean my baby has Down syndrome?

No, an abnormal nuchal translucency scan doesn’t diagnose anything. It can mean your child is at a higher risk of having Down syndrome. Healthcare providers prefer to use a blood test in addition to the NT scan. That’s because it’s a more accurate assessment of the risk.

Do I need both NIPT and NT?

No. But you should talk to your healthcare provider before making any decisions on which screenings to have. They can help you understand the pros and cons of each. They can also help you figure out which one might be best for you. Things like health history, insurance and risk factors can play a role in your decision. The main difference is that NIPT is a blood test, while NT is an ultrasound.