Nuchal Translucency/Early Anatomy Ultrasound
A nuchal translucency ultrasound measures the fluid at the back of a baby’s neck between 11 and 14 weeks of pregnancy.
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.
When during pregnancy is the ultrasound performed?
The test is performed at Mount Sinai between 11 weeks, 2 days and 13 weeks, 3 days of the 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.
Before your appointment
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 ultrasound with results from at least one blood test. Methods include:
The advantage of the FTS is speed, with results of both the ultrasound and screening forwarded directly to your health care provider within 7-10 days. This allows for earlier diagnostic testing (CVS) and decision making.
The IPS results take longer, as the screening includes an additional blood test in the second trimester, but it is more accurate, and has a lower false positive rate, meaning fewer women will be offered an unnecessary amniocentesis (carrying a 0.5 - 1 per cent risk of miscarriage).
Before the ultrasound, you will be asked to sign an optional consent form to allow us to collect information on your pregnancy. This helps us evaluate the performance of our tests and continue to develop and enhance prenatal care for pregnant women. Consent is your choice and does not affect your medical or pregnancy care.
The ultrasound itself will take about 20 minutes to perform.
Once finished, you will be directed towards our laboratory to have blood drawn for whichever screening method you have chosen.
How long will the appointment take?
This is difficult to accurately estimate - the timing of both the ultrasound and the blood test is variable and often unpredictable.
A typical appointment takes approximately 3 hours, but can be longer if complications are found and/or counselling is required for either you or for individuals having their examination before you.
It is important to note that not all pregnancies with Down syndrome or other chromosome problems show a high fluid measurement in test results.
In most cases, the results of your ultrasound and screening will be forwarded to your health care provider when they are available, depending on which screening method you've chosen.
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 counsellor as soon as possible to discuss what your results mean, and what your options are for further testing.
Additional tests include:
- a detailed fetal ultrasound at 18 to 20 weeks
- an ultrasound of the baby’s heart (called echocardiogram)
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 a twin pregnancy, we normally expect twice the amount of a given protein or hormone compared to a single pregnancy. But if one baby can be making a large amount of the protein/hormone typically measured in a single pregnancy and the other can make 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.
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.
We are currently conducting research into developing a better screening test that can combine information obtained from a blood test and the nuchal translucency ultrasound for twins/triplets.
If you are carrying twins or triplets, and you would be willing to participate in the development of this test, we will provide you with a requisition for your blood to be drawn for this purpose.
Other things this early ultrasound can tell you
- it confirms the dating of your pregnancy
- it provides reassurance that the baby is developing appropriately at this stage
- it detects pregnancies with more than one baby and, very importantly, determines whether the babies have the same placenta or not, 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.
Coming for your appointment
Your nuchal translucency ultrasound appointment will be at:
The Lawrence and Frances Bloomberg Department of Obstetrics and Gynaecology
700 University Avenue, 3rd Floor
Toronto, Ontario M5G 1Z5
Please register at Main Reception to obtain a Mount Sinai Hospital Card if you do not already have one. Then check in with the Ultrasound Department opposite from Main Reception area.