Nuchal Translucency/Early Anatomy Ultrasound

NUCHAL TRANSLUCENCY ULTRASOUND

What does this procedure involve?

A nuchal translucency (NT) ultrasound measures the fluid at the back of a baby’s neck between 11 and 14 weeks of pregnancy. The ultrasound itself will take about 20 minutes to perform. Before you arrive for your appointment we strongly encourage you to decide which screening test you would like to use to assess the results of your ultrasound.
Screening tests combine the measurements from the NT ultrasound with results from at least one blood test. Methods include: First trimester screening (FTS) or Integrated Prenatal Screening (IPS).
The time required to complete the ultrasound and blood test is variable. A typical appointment takes approximately 3 hours, but can be longer if complications are found and/or counseling is required for either you or for individuals having their examination before you.

What does this test measure?

A nuchal translucency ultrasound measures the amount of fluid at the back of a baby’s neck. All babies have some fluid there, but babies with chromosome abnormalities such as Down syndrome, Trisomy 13, and Trisomy 18, tend to have an unusually high amount.

The most common explanation for a higher fluid level is some variation in normal development, but it can also indicate heart defects and certain rare genetic syndromes.

What else can this ultrasound tell me?
  • It confirms the dating of your pregnancy.
  • It provides reassurance that the baby is growing appropriately at this stage.
  • It detects pregnancies with more than one baby and, very importantly, determines whether the babies have the same placenta (identical twins) or not (fraternal twins), which is very helpful in caring for these pregnancies.
  • It provides an initial assessment of the anatomy that is visible, as some birth defects can be detected at this stage.
  • Given that many problems cannot be detected at this stage, an ultrasound at 18-20 weeks is recommended and can be arranged by your health care provider.
When can this screening test be done?

The test is performed at Mount Sinai hospital between 11 and 14 weeks of pregnancy. Measurements taken during the test are based on the crown-rump length of the baby, which is calculated by the ultrasound machine. Measurements taken outside the stated time frame generally cannot be used for screening tests.

When will the results be available?

Your doctor’s office will receive an ultrasound report, including the NT measurement within a few days following your ultrasound appointment. If there is any concern about your NT result your physician will inform you and you may seek a genetic counsellor.

What kind of results should I expect?

It is important to note that not all pregnancies with Down syndrome or other chromosome problems show an increased nuchal translucency. If your measurement is above the limit considered normal, or another unexpected complication is evident from the test, you will be offered an appointment with a genetic counselor as soon as possible to discuss what your results mean, and what your options are for further testing.

Additional tests include:
  • CVS or amniocentesis
  • A detailed fetal ultrasound at 18 to 20 weeks
  • An ultrasound of the baby’s heart (called echocardiogram)
  • What if I am having twins or triplets?

Women pregnant with twins or triplets will not require a blood test as we currently are not using blood tests to screen for Down syndrome (or Trisomy 13/18) in multiple pregnancies. In a twin pregnancy, we normally expect twice the amount of a given protein or hormone compared to a single pregnancy. But if one baby is making a large amount of the protein or hormone typically measured in a single pregnancy and the other is making a small amount, this will lead to an inaccurate result. Thus, the best screening for a multiple pregnancy is the use of each nuchal translucency measurement as it is unique to each baby, and combining it with the maternal age-related risk. We will aim to provide your estimate after your ultrasound. When we are not able to do this, we will contact you and your health care provider once the information is available.

 

Special Pregnancy Program

Referrals »

Fetal Medicine: 416-586-4800 x 7756
Fax: 416-586-3216

Maternal Medicine: 416-586-4800 x 7000
Fax: 416-586-5109

Main clinic hours: Monday to Friday, 8am to 4pm

Prenatal Diagnosis & Medical Genetics

Referrals »

phone: 416-586-4800 x 4523
fax numbers:
416-586-4723 or 416-586-8384

Perinatal Mental Health

Referrals »

Phone: 416-586-4800 x 8325
Fax: 416-586-8596