Nuchal translucency test

Definition

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 for Down syndrome and other genetic problems in the baby.

Alternative Names

Nuchal translucency screening; NT; Nuchal fold test; Nuchal fold scan; Prenatal genetic screening; Down syndrome - nuchal translucency

How the Test is Performed

Your health care provider uses abdominal ultrasound or a vaginal 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 abdominal ultrasound picture. You may be asked to drink 2 to 3 glasses of liquid an hour before the test. DO NOT urinate before your ultrasound.

If a vaginal ultrasound is performed, your bladder should be empty.

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 provider may advise this test to screen your baby for Down syndrome. Many pregnant women decide to have this test.

Nuchal translucency is usually done between the 11th and 14th week of pregnancy. It can be done earlier in pregnancy than amniocentesis. Amniocentesis is another test that checks for birth defects.

Normal Results

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.

Nuchal translucency measurement increases with gestational age. This is the period between conception and birth. The higher the measurement compared to babies the same gestational age, the higher the risk is for certain genetic disorders.

A measurement of up to 3 mm is considered a low risk for genetic disorders. However, different clinics may use slightly different numbers based on their experience.

What Abnormal Results Mean

More fluid than normal in the back of the neck means there is a higher risk for Down syndrome, trisomy 18, trisomy 13, Turner syndrome, or congenital heart disease. But it does not tell for certain that the baby has Down syndrome or another genetic disorder. A diagnostic test is required to find out if a serious genetic disorder is present.

The nuchal translucency test is a screening test. It does not screen for genetic problems in babies. It is helpful in deciding who may need further testing. An abnormal result would then require follow up of a diagnostic test such as an amniocentesis or non-invasive prenatal test (NIPT).

Risks

There are no known risks from ultrasound.

References

American College of Obstetricians and Gynecologists website. NIPT summary of recommendations. www.acog.org/advocacy/policy-priorities/non-invasive-prenatal-testing/current-acog-guidance. Accessed June 7, 2023.

Driscoll DA, Simpson JL. Genetic screening and diagnosis. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 10.

Dugoff L, Wapner RJ. Prenatal diagnosis of congenital disorders. In: Lockwood CJ, Copel JA, Dugoff L, et al, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2023:chap 30. 

Walsh JM, D'Alton ME. Nuchal translucency. In: Copel JA, D'Alton ME, Feltovich H, et al, eds. Obstetric Imaging: Fetal Diagnosis and Care. 2nd ed. Philadelphia, PA: Elsevier; 2018:chap 45.