Nuchal Translucency: Tests, Results, and Reliability

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During a test for nuchal translucency (NT), an ultrasound is performed to measure the collection of fluid between the fetus’s spine and the skin in the area of the nape of the neck. The procedure is performed by a specially trained ultrasound technician, and the results are read by a radiologist who also has specific training.

This test differs from a routine ultrasound and is not offered at every healthcare facility. Rather, it generally must be scheduled at a university medical center or another specialized facility.

When the results of the nuchal translucency screening are positive, there is cause for concern, but it does not necessarily indicate a congenital defect is present. Rather, other diagnostic tests may be needed—such as amniocentesis (an evaluation of the fluid in the amniotic sac that surrounds the fetus) or chorionic villus sampling (a test for serious chromosome disorders).

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Purpose

NTs are conducted to assess the nuchal folds on the back of the fetus’s neck. By measuring the thickness of the nuchal folds—an indicator of how much fluid there is inside the folds—the risk of possible issues with the fetus, including Down syndrome, can be detected.

The test does not provide a definitive diagnosis and does have a significant margin of error, so a blood test might also be done. Blood is drawn from the mother, and the two results are combined to provide more information about the baby.

Ultrasound Preparation

Before the ultrasound, it’s usually advised for the mother to have a full bladder. This enhances the movement of sound waves in the abdomen, allowing the technician a clearer view of the structures. The nuchal translucency ultrasound may be performed:

  • Transabdominally (from the outside of the abdomen)
  • Transvaginally (inserted into the vagina)

Test Results

Combined first-trimester screening—including the ultrasound, a PAPP-A, and an hCG test—does not enable the healthcare provider to make a diagnosis of Down syndrome. Rather, information is gathered to come up with a probability factor that can indicate whether there is a risk of chromosomal disorders or provide reassurance that the fetus is at low risk for these defects.

Information collected includes:

  • A person’s age
  • Ultrasound
  • Bloodwork

Calculating Risk

A specific mathematical calculation will be employed to consider the outcome of the nuchal translucency screening, together with the results of the maternal PAPP-A and hCG blood tests.

A numeric risk (including the probability factor) will be assigned. If the numeric probably is one in 230 or higher, it’s considered a positive screen.

If a person has a positive screening, a genetic counselor or clinician is assigned to help interpret what the results mean and to help offer choices about options for further testing.   

Screening Reliability

There is an 80% accuracy rate in NT screening. When NT screening is combined with beta hCG and PAPP-A blood tests, that rate increases to 90%.

Recent studies have shown that when these three screening tests are further combined with an examination of the fetal nasal bones, as well as an evaluation of fetal blood flow through certain areas of the heart (ductus venous flow and tricuspid flow), the accuracy rate rises to 95%.

Frequently Asked Questions

How much does a nuchal translucency test cost?

According to USC Fertility at the Keck School of Medicine, a nuchal translucency ultrasound costs approximately $500.

It may not be covered by insurance because this type of genetic testing is not standard for pregnant people of all ages. Rather, it’s more common in those over 35 who have a higher risk of birth defects.

When is nuchal translucency screening done?

The test is usually performed during the first or early second trimester of pregnancy, between weeks 11 and 13.

How long does a nuchal translucency ultrasound take?

The procedure usually takes between 20 and 40 minutes.

A Word From Get Meds Info

Undergoing screening tests—such as the nuchal translucency screening—is no small undertaking. Every pregnant person wants to know without the shadow of a doubt that their baby is perfectly healthy.

Keep in mind that early screening tests, such as the nuchal translucency screening, do not definitively prove anything. They only indicate that more definitive tests are required before any type of diagnosis can be made.

If you have had a positive test screening and your OB-GYN healthcare provider has not already done so, be sure to ask about a consultation with a genetic counselor to help you through the process. Remember that early screening is all about choices, and choices help empower you to make the best decisions for you and your baby. 

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