Nuchal Translucency Screening Test
The nuchal (say "NEW-kuhl") translucency screening is a test done during pregnancy. It uses ultrasound to measure the thickness of the fluid buildup at the back of the developing baby's neck. If this area is thicker than normal, it can be an early sign of Down syndrome , trisomy 18 , or heart problems.
This test shows the chance that a baby may have a certain problem. It can't show for sure that a baby has a problem. You would need a diagnostic test, such as chorionic villus sampling (CVS) or amniocentesis, to find out for sure if the baby actually has a problem.
Why It Is Done
A nuchal translucency test is done to find out the chance that your developing baby (fetus) may be at risk for having Down syndrome or other problems.
How To Prepare
You may need a full bladder for the nuchal translucency test. If so, you'll be asked to drink water or other liquids just before the test and to avoid urinating before the test.
Talk with your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?) .
How It Is Done
Most often, a nuchal translucency test is done by a specially trained ultrasound technologist. But it may be done by a radiologist or an obstetrician who has received special training to do this test.
Often you don't need to remove your clothes for the test. You can lift your shirt and push down the waistband of your skirt or pants. If you're wearing a dress, you'll be given a cloth or paper covering to put over your legs during the test.
If you need a full bladder for the test, tell your doctor or ultrasound technologist if your bladder is so full that you're in pain.
During the test:
- You'll lie down on your back or on your side on an exam table.
- A gel will be spread on your belly.
- A small, handheld device called a transducer will be pressed against the gel on your skin and moved over your belly. Images of the baby are displayed on a monitor. The technologist or doctor will look for and measure the thickness of the fluid buildup at the back of the baby's neck.
When the test is done, the gel is wiped off your skin. You can urinate as soon as the test is done.
The test usually takes about 15 to 20 minutes.
How It Feels
During a nuchal translucency test, you may have a feeling of pressure in your bladder. The gel may feel cool when it is first put on your belly. You'll feel a light pressure from the transducer as it passes over your belly.
There are no known risks linked with a nuchal translucency test, either to you or the baby. But you may feel anxious if the test shows there is an increased chance that your baby may have a problem.
Ultrasound is a safe way to check for problems and get information about your developing baby. It doesn't use X-rays or other types of radiation that may harm the baby.
Your doctor will look at the results of the nuchal translucency test to see if the area at the back of the baby's neck is thicker than normal.
2.5 millimeters (mm) or less
More than 2.5 mm
You may not receive information about the test right away. Full results are usually available in 1 or 2 days.
How accurate is the test?
The nuchal translucency test can find out if your developing baby (fetus) is at higher-than-normal risk for problems. But it can't tell for sure that the baby has a problem. You would need another test, called a diagnostic test, to make sure.
The accuracy of this test is based on how often the test correctly finds a problem. For example:
- The nuchal translucency test correctly finds Down syndrome in 64 to 70 out of 100 fetuses who have it. It misses Down syndrome in 30 to 36 out of 100 fetuses. 2
- First-trimester screening (nuchal translucency combined with blood tests) correctly finds Down syndrome in 82 to 87 out of 100 fetuses who have it. But these tests miss it in 13 to 18 out of 100 fetuses. 2
- The integrated screening test (first-trimester tests plus the triple or quad screening blood tests in the second trimester) correctly finds Down syndrome in about 95 out of 100 fetuses who have it. This means that the test misses Down syndrome in 5 out of 100 fetuses. 2
What Affects the Test
Nuchal translucency test results may be affected by:
- Being overweight or obese.
- Stool (feces) or air in the intestines or rectum.
- An abnormally low amount of amniotic fluid.
- Not being able to lie still during the test.
- The fetus being in certain positions during the test.
- A very active fetus.
What To Think About
It's possible that a screening test will show that the baby has an increased chance of having a problem when he or she doesn't have the problem. This is called a false-positive test result. And it's also possible that a screening may show that the baby doesn't have a problem when he or she does. This is called a false-negative test result.
Other Places To Get Help
|American Congress of Obstetricians and Gynecologists (ACOG)|
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- American College of Obstetricians and Gynecologists (2007, reaffirmed 2011). Screening for fetal chromosomal abnormalities. ACOG Practice Bulletin No. 77. Obstetrics and Gynecology, 109(1): 217-227.
Other Works Consulted
- Bianchi DW (2010). Prenatal genetic diagnosis. In CA Gleason, SU Devaskar, eds., Avery's Diseases of the Newborn, 9th ed., pp. 180-185. Philadelphia: Elsevier Saunders.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
|Sarah Marshall, MD - Family Medicine|
|Siobhan M. Dolan, MD, MPH - Reproductive Genetics|
|Last Revised||November 6, 2012|
Last Revised: November 6, 2012
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