The nuchal translucency test measures the nuchal fold thickness. This is an area of tissue at the back of an unborn baby's neck. Measuring this thickness helps assess the risk of Down syndrome and other genetic problems in the baby.
Your health care provider will use ultrasound to measure the nuchal fold. All unborn babies have some fluid at the back of their neck. In a baby with Down syndrome or other genetic disorders, there is more fluid than normal. This makes the space look thicker.
A blood test of the mother is also done. Together, these two tests will tell if the baby could have Down syndrome or another genetic disorder.
How to Prepare for the Test
Having a full bladder will give the best ultrasound picture. You may be asked to drink two to three glasses of liquid an hour before the test. Do not urinate before your ultrasound.
How the Test will Feel
You may have some discomfort from pressure on your bladder during the ultrasound. The gel used during the test may feel slightly cold and wet. You will not feel the ultrasound waves.
Why the Test is Performed
Your health care provider may recommend this test to screen your baby for Down syndrome. Many pregnant women decide to have this test.
This test can be done earlier in pregnancy than amniocentesis (another test that checks for birth defects). Nuchal translucency is usually done between the 11th and 14th week of pregnancy.
A normal amount of fluid in the back of the neck during ultrasound means it is very unlikely your baby has Down syndrome or another genetic disorder.
A normal measurement at 11 weeks is up to 2 millimeters (mm).
A normal measurement at 13 weeks, 6 days is up to 2.8 mm.
What Abnormal Results Mean
More fluid than normal in the back of the neck means there is a higher risk of Down syndrome. But it does not tell for certain that the baby has Down syndrome.
If the result is abnormal, other testing can be done. Most of the time, the other test done is amniocentesis.
There are no known risks from ultrasound.
Bromley B, Benacerraf B. Chromosomal abnormalities. In: Rumack CM, Wilson SR, Charboneau JW, Levine D. Diagnostic Ultrasound. 4th ed. Philadelphia, PA: Elsevier Mosby; 2010:chap 31.
Simpson JL, Holzgreve W, Driscoll DA. Genetic counseling and genetic screening. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 10.
Cynthia D. White, MD, Fellow American College of Obstetricians and Gynecologists, Group Health Cooperative, Bellevue, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.