What You Should Know About Nuchal Translucency Testing

During pregnancy, you have a variety of options for prenatal testing—some are screening tests and some are diagnostic tests. What’s the difference? Prenatal screening tests tell you the chances that the fetus has any anomalies (irregularities), whereas prenatal diagnostic tests can tell you whether the fetus actually has a certain condition.

Various tests are done during each trimester, including a nuchal translucency screening. A nuchal translucency screening test is typically done during the first trimester between weeks 11 and 13.

Some people opt to have prenatal screening tests, while others do not. This is a personal decision and one that should be made after collecting the information about what each test does and how it may fit into your decision-making. If you’re not sure about a test, talk it over with your partner, care provider, or a genetic counselor.

Overview

A nuchal translucency (NT) test uses abdominal ultrasound to measure the nuchal fold thickness of the fetus. The nuchal folds are on the back of the fetus’s neck, and measuring the thickness of the nuchal folds—an indicator of how much fluid there is inside the folds—can provide information on possible issues with the fetus, including Down syndrome.

In Down syndrome and other genetic disorders, there is more fluid than normal and thus the thickness of these folds is increased. The test does have a significant margin of error, so a blood test might also be done. Blood is drawn from the mother and the two results are combined to provide more information about your baby. Further testing can yield more definitive results.

It’s important to remember that this is a screening test—if you get an abnormal result, this doesn’t necessarily indicate any disorder present in your baby.

Process

The nuchal translucency test is, at its core, an abdominal ultrasound. You will be asked to make sure your bladder is filled, since this will help provide a good picture. (Do not empty your bladder before the appointment.) A gel will be applied to your abdomen to assist the transducer, a wand-like instrument, in transmitting the sound waves through your uterus and also in receiving them.

You might experience some pressure during the test or feel uncomfortable while the technician is pressing on your belly with a full bladder, but the test is not painful at all and carries no risks to you or the baby. It is a noninvasive test and can be done right in your obstetrician or midwife’s office.

The Results

The nuchal translucency measurements increase with gestational age, so the measurements are compared to other babies the same gestational age. If the measurement is within normal limits, it is unlikely that any genetic disorder is present. Normal measurements for the NT are:

  • Eleven weeks (fetus is up to 2 millimeters in size)
  • Thirteen weeks, six days (fetus is up to 2.8 millimeters in size)

If there is more fluid than is typical, there is a higher risk of certain disorders, including Down syndrome, various trisomies, Turner syndrome, or congenital heart disease.

Since the NT is a screening test, your obstetrician may recommend a diagnostic test like amniocentesis or other tests to ascertain if there is a definite anomaly.

It’s important to remember that a normal result on the NT test does not guarantee that your baby does not have any chromosomal abnormalities or any other issues, and an abnormal result on the NT test does not definitively mean your baby has any anomalies. Screening tests merely give you information about how likely it is that there may be an issue present. Diagnostic tests can provide you with more accurate information about your baby.

Talk with your healthcare provider about what your results mean. If they are abnormal, ask what this may signify and what kinds of tests can be done to get a more definitive diagnosis. You might want to seek out a genetic counselor who can help advise you on the various diagnoses that the NT screens for, what each of these entails, what your options are, and what diagnostic tests are available.

Your provider and the genetic counselor can also discuss with you the risks and benefits of each diagnostic test, and which one might be best for you.

 

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