University of California San Francisco | About UCSF | UCSF Benioff Children's Hospital San Francisco
Search Site | Find a Doctor

Nuchal Translucency Test

Definition

Nuchal translucency is the thickness at the back of an unborn baby's neck. Measuring this thickness helps assess the risk of Down syndrome.

How the Test Is Performed

Your health care provider will use ultrasound to measure the thickness at the back of the baby's neck. All babies have some fluid at the back of their neck, but in Down syndrome 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.

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 on the ultrasound wand 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 11 and 14 weeks of pregnancy.

A nuchal pregnancy test detects only Down syndrome. It does not detect neural tube defects or other birth defects.

Normal Values

A normal amount of fluid in the back of the neck during ultrasound means that it is very unlikely your baby has Down syndrome.

  • A normal measurement at 11 weeks is up to 2 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 greater risk of Down syndrome. However, 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.

What the risks are

There are no known risks from ultrasound. Ultrasound does not involve radiation, like x-rays do.

References

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: Saunders Elsevier; 2012:chap 10.

Review Date: 8/25/2012

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2010 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.

Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.