Nuchal Translucency (NT) Scan: What It Is and How It Screens for Chromosomal Conditions
The Nuchal Translucency Test, or NT test, performed between 11 weeks and 13 weeks, is a prenatal screening ultrasound performed during early pregnancy to assess the risk of chromosomal and structural issues in a growing foetus. It measures the thickness of a fluid-filled space located at the back of the neck, known as nuchal translucency. Every foetus has fluid in the back of the neck during early pregnancy.
An increased thickness of these spaces is associated with a higher risk of chronic conditions such as Down syndrome (Trisomy 21), Edward syndrome (Trisomy 18), and Patau Syndrome (Trisomy 13) and some other heart and structural defects. NT scans do not detect these conditions, it estimates the risk and probability that a foetus may develop these risks. The NT test is a non-invasive procedure and poses no risk for either the mother or the baby.
Why is the NT Test Done
The Nuchal Translucency Test in pregnancy is important to assess the early risk of chromosomal and structural defects that a foetus might develop. NT tests assess the probability of the risks long before symptoms or signs start to appear. The NT test is mainly performed to screen for chromosomal abnormalities, including Down syndrome, Edwards syndrome, and Patau Syndrome.
Foetuses affected by these chromosomal conditions may accumulate more fluid at the back of the neck during the first trimester. Measuring the thickness of this fluid, along with maternal factors and biochemical markers, helps doctors estimate the risk of these conditions in early pregnancy.
Increased nuchal translucency measurement also indicates structural defects in the foetus. It doesn't diagnose the problems, but it signals the risk that the foetus may develop. Increased NT thickness may show the risk of cardiac problems, genetic syndromes, and rare skeletal or developmental conditions.
Benefits of the Nuchal Translucency Test
NT tests, along with maternal age, NT measurement, and blood markers, help easily identify the likelihood of the issues the foetus will develop, and you will get enough time to look for solutions.
Finding the problems early gives more time to process, seek counselling, and prepare for treatment. You can take informed decisions, prepare for treatment, and mentally prepare yourself.
When is a Nuchal Translucency Scan Performed
The NT scan is conducted to measure the fluid-filled space in the back of the neck of the foetus, which is between 45 mm and 84 mm crown-rump length. This test is typically taken during 11 to 13 weeks and 6 days of pregnancy. Performing tests before or after is not reliable.
During foetal development, a small amount of fluid naturally accumulates under the skin at the back of the foetal neck. If the baby is at risk of chromosomal or structural defects, the fluid accumulates more due to late lymphatic drainage, cardiac issues, or altered connective tissue development. During weeks 11 to 16 and 6 days, the fluid is mostly visible, making it easy to predict risks.
Nuchal Translucency Test Procedure
An NT scan is a non-invasive ultrasound procedure that may take 20-45 minutes to perform. It involves accurate imaging to measure fluid at the back of the foetal neck. You can see the screen in real time during the procedure.
Preparation
Patients should go with a full bladder to elevate the uterus, displacing bowel gas for a clear abdominal view.
Ultrasound
NT scan can be performed by 3 methods depending on the gestation, body habitus, and foetal position.
What Technicians Look For
During the scan, sonographers look for:
How the Nuchal Translucency is Measured
The NT scan measures the maximum thickness of the fluid space between the skin at the back of the foetal neck and the soft tissue over the cervical spine. To ensure precision, the measurement is taken at the widest point, perpendicular to the spine. Callipers are placed edge-to-edge. The test is repeated 3 times to record accurate values.
Interpreting NT Result
The NT result involves comparing the measured fluid thickness at the foetal neck to gestational age. NT measurement is combined with maternal age and first-trimester blood markers to predict the accuracy of the result.
The Nuchal Translucency Test is not a diagnosis. Even if the measurement is abnormal or increased, your doctors might recommend other diagnostic tests, including Chorionic Villus Sampling or amniocentesis. CVS is performed between 11 and 14 weeks and provides accurate chromosomal information. Amniocentesis is performed after 15 weeks and provides an accurate genetic diagnosis. An NT scan is a safe test which provides risk and probability for expectant parents to make the right decisions.
An increased thickness of these spaces is associated with a higher risk of chronic conditions such as Down syndrome (Trisomy 21), Edward syndrome (Trisomy 18), and Patau Syndrome (Trisomy 13) and some other heart and structural defects. NT scans do not detect these conditions, it estimates the risk and probability that a foetus may develop these risks. The NT test is a non-invasive procedure and poses no risk for either the mother or the baby.
Why is the NT Test Done
The Nuchal Translucency Test in pregnancy is important to assess the early risk of chromosomal and structural defects that a foetus might develop. NT tests assess the probability of the risks long before symptoms or signs start to appear. The NT test is mainly performed to screen for chromosomal abnormalities, including Down syndrome, Edwards syndrome, and Patau Syndrome.
Foetuses affected by these chromosomal conditions may accumulate more fluid at the back of the neck during the first trimester. Measuring the thickness of this fluid, along with maternal factors and biochemical markers, helps doctors estimate the risk of these conditions in early pregnancy.
Increased nuchal translucency measurement also indicates structural defects in the foetus. It doesn't diagnose the problems, but it signals the risk that the foetus may develop. Increased NT thickness may show the risk of cardiac problems, genetic syndromes, and rare skeletal or developmental conditions.
Benefits of the Nuchal Translucency Test
NT tests, along with maternal age, NT measurement, and blood markers, help easily identify the likelihood of the issues the foetus will develop, and you will get enough time to look for solutions.
Finding the problems early gives more time to process, seek counselling, and prepare for treatment. You can take informed decisions, prepare for treatment, and mentally prepare yourself.
When is a Nuchal Translucency Scan Performed
The NT scan is conducted to measure the fluid-filled space in the back of the neck of the foetus, which is between 45 mm and 84 mm crown-rump length. This test is typically taken during 11 to 13 weeks and 6 days of pregnancy. Performing tests before or after is not reliable.
- Before 11 weeks: The foetus is too small,l and the fluid may be clear.
- After 13 weeks: The excess fluid is absorbed into the lymphatic system, which makes the Nuchal space less visible. When the lymphatic system starts to develop, it reduces the translucency.
During foetal development, a small amount of fluid naturally accumulates under the skin at the back of the foetal neck. If the baby is at risk of chromosomal or structural defects, the fluid accumulates more due to late lymphatic drainage, cardiac issues, or altered connective tissue development. During weeks 11 to 16 and 6 days, the fluid is mostly visible, making it easy to predict risks.
Nuchal Translucency Test Procedure
An NT scan is a non-invasive ultrasound procedure that may take 20-45 minutes to perform. It involves accurate imaging to measure fluid at the back of the foetal neck. You can see the screen in real time during the procedure.
Preparation
Patients should go with a full bladder to elevate the uterus, displacing bowel gas for a clear abdominal view.
- Wear comfortable and loose clothes for easy access.
- Clear ultrasound gel will be applied to the abdomen to improve image clarity.
Ultrasound
NT scan can be performed by 3 methods depending on the gestation, body habitus, and foetal position.
- Transabdominal Ultrasound: It is the most common one, where the gel is applied to the lower abdomen, and a handheld transducer glides with sliding or rotating motions. It's non-invasive and comfortable.
- Transvaginal Ultrasound: It involves inserting a thin, lubricated probe into the vagina. It is usually conducted on an obese patient if the uterus is low-lying or the abdominal view is not clear.
What Technicians Look For
During the scan, sonographers look for:
- Foetal Position: Neutral neck, mid-sagittal view showing nose tip, palate rectangle, and diencephalon.
- Length: Crown-rump length to confirm gestational age.
How the Nuchal Translucency is Measured
The NT scan measures the maximum thickness of the fluid space between the skin at the back of the foetal neck and the soft tissue over the cervical spine. To ensure precision, the measurement is taken at the widest point, perpendicular to the spine. Callipers are placed edge-to-edge. The test is repeated 3 times to record accurate values.
Interpreting NT Result
The NT result involves comparing the measured fluid thickness at the foetal neck to gestational age. NT measurement is combined with maternal age and first-trimester blood markers to predict the accuracy of the result.
- Normal Results: Normal NT measurement means the fluid thickness at the back of the foetal neck falls within the expected range for the baby’s gestational age and size. It suggests that the probability of chromosomal conditions is reduced.
- Abnormal Result: Increased NT measurement shows the thickness of the space is more than expected for the gestational age. It is associated with chromosomal abnormalities, congenital heart defects, genetic syndromes, and structural or developmental conditions.
The Nuchal Translucency Test is not a diagnosis. Even if the measurement is abnormal or increased, your doctors might recommend other diagnostic tests, including Chorionic Villus Sampling or amniocentesis. CVS is performed between 11 and 14 weeks and provides accurate chromosomal information. Amniocentesis is performed after 15 weeks and provides an accurate genetic diagnosis. An NT scan is a safe test which provides risk and probability for expectant parents to make the right decisions.
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