A small, handheld device called a transducer will be pressed against the gel on your skin and moved over your belly. Images of the baby are displayed on a monitor. The technologist or doctor will look for and measure the thickness of the fluid buildup at the back of the baby's neck. The test usually takes about 15 to 20 minutes.
How It Feels During a nuchal translucency test, you may have a feeling of pressure in your bladder. Risks There are no known risks linked with a nuchal translucency test, either to you or the baby.
Results Your doctor will look at the results of the nuchal translucency test to see if the area at the back of the baby's neck is thicker than normal. Nuchal translucency test footnote 1 Normal: 2. How accurate is the test? The accuracy of this test is based on how often the test correctly finds a problem. For example: The nuchal translucency test correctly finds Down syndrome in 64 to 70 out of fetuses who have it.
It misses Down syndrome in 30 to 36 out of fetuses. But these tests miss it in 13 to 18 out of fetuses. This means that the test misses Down syndrome in 4 out of fetuses. What Affects the Test Nuchal translucency test results may be affected by: Being overweight or obese.
Stool feces or air in the intestines or rectum. An abnormally low amount of amniotic fluid. Not being able to lie still during the test. The fetus being in certain positions during the test. A very active fetus. What To Think About Talk with your doctor about any concerns you have.
A Manual of Laboratory and Diagnostic Tests , 9th ed. Philadelphia: Wolters Kluwer Health. American College of Obstetricians and Gynecologists Screening for fetal aneuploidy. Obstetrics and Gynecology , 5 : e—e DOI: Accessed April 6, Pre-Natal Testing. Genetic Services. Genetic Counselling Genetic Carrier Screening.
Pregnancy Ultrasounds. Fertility Services. Available Procedures. Full Listing of Procedures Performed. Genetic Counsellor Awareness Day. The First Scan of Pregnancy: What comes next? Debunking Ultrasound Myths. Pregnancy in the information age. Nuchal Translucency Screening. Screening for Down syndrome in early pregnancy. What is Down syndrome? T1 weeks. What does a nuchal translucency screening for Down syndrome involve?
The test has two parts:. Part 2: An Ultrasound. Part 1 — Blood Test. Part 2 — Ultrasound. A change in the level of these proteins may indicate that there is an increased chance that the baby has Down syndrome or other common trisomy. The ultrasound can be done by our specially trained sonologist or sonographer between They've also calculated the statistical relationship between this measurement, the baby's age, the mother's age, and the likelihood that the baby will be born with certain abnormalities.
In general, the thicker the nuchal translucency at a given gestational age, the higher the chance of a chromosomal problem. You may get the results right away, or you may have to wait up to 10 days if the doctor has to send the data to a processing center. You'll want to talk with your practitioner or a genetic counselor about how to interpret the results, which can be confusing.
Many centers will report each individual lab result as well as the final calculated result using a special formula. You'll get your results in the form of a ratio that expresses your baby's chances of having a chromosomal defect. For example, a risk of 1 in means that for every women with this result, one baby will have Down syndrome and 99 will not. A risk of 1 in 1, means that for every 1, women with this result, one baby will have it and 1, will not.
The higher the second number, the lower the risk. You may also be told that your results are "normal" or "abnormal" for a particular condition, depending on whether the ratio is below or above a specified cutoff. For example, some tests use a cutoff of 1 in So a result of 1 in 1, would be considered normal because the risk that there's a problem is lower than 1 in A ratio of 1 in would be considered abnormal because that risk is higher than 1 in Remember that a normal screening result screen negative isn't a guarantee that your baby has normal chromosomes, but it does suggest that a problem is unlikely.
Likewise, an abnormal screening result screen positive doesn't mean that your baby has a chromosomal problem — just that your baby is more likely to have one. Most screen-positive babies turn out not to have a problem: Only about a third of babies with an increased nuchal translucency measurement turn out to have chromosomal defects. The NT scan alone will detect about 70 to 80 percent of babies with DS depending on which study you look at. The detection rate for the NT scan plus a first-trimester blood test ranges from 79 to 90 percent.
Most tests will include both the NT scan and the blood test. This does not mean that a screen-positive baby has a 79 to 90 percent chance of having DS.
It just means that 79 to 90 percent of babies who have DS will have screening results that are suspicious enough to recommend diagnostic testing. And 5 to 21 percent of babies who have DS will be determined to be at normal risk — that is, the results will be misleading. Screening tests aren't perfect.
They don't detect all cases of DS, so they may identify your baby as being at low risk when they really do have DS. In other words, if you're carrying a baby with DS, there's a 79 to 90 percent chance that the combined screening will detect the abnormality and give you what's called a screen-positive result indicating that further testing is recommended.
But it also means there's a 5 to 21 percent chance that the tests will miss the DS and give you a screen-negative result. This is called a false negative result, and it might lead you to decide against diagnostic testing that would have revealed a problem. These tests also have a 5 percent false-positive rate. A false-positive result is one that suggests that your baby is at increased risk for DS or another condition when, in fact, there's no problem.
With the help of your practitioner or a genetic counselor , you'll want to decide whether the results indicate a high enough risk that you want to have CVS or amniocentesis to get a definitive diagnosis.
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