Nuchal Translucency (NT) Scan is a part of the ultrasound scan done at 12 weeks of pregnancy. The scan reveals the risk of chromosomal abnormalities in infants. It tells us if there is any probability of having Down syndrome, Edwards syndrome, or Patau Syndrome.
The approximate cost of the NT scan in India varies from INR 600 to 4000. This cost variation depends upon the city, the doctor's fees, the patient's overall medical condition, the hospital's type, and many other factors.
Before undergoing the NT scan, the doctor will measure the size of the nuchal fold at the back of the baby's neck.
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What is the Nuchal Fold?
A nuchal fold is just a skin fold observed at the back of the neck of the fetus during the second trimester of pregnancy. If the thickness of the fold is increased, it indicates fetal anomalies, which can be detected by second-trimester ultrasound.
Why is the NT Scan Done?
The scan focuses on the thickness of the nuchal fold. The thickness indicates chromosomal abnormalities, but we cannot confirm it. The test is performed between 11 and 14 weeks of pregnancy.
The scan can be done through the abdomen or sometimes by inserting a probe through the vagina. Sometimes, a blood test may also be needed along with the NT scan.
The NT scan is most commonly linked with Down's Syndrome. Down's Syndrome is a genetic disorder caused by cell division leading to an extra copy of chromosome 21. This is responsible for changes in the developmental and physical features of the body. Some of the most common signs and symptoms include a smaller head, flat face, short hands and fingers, smaller ears, poor muscle tone, short height, etc.
How Does an NT Scan Work?
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During the screening, either a doctor or a technician will conduct an abdominal ultrasound.
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Another option is a transvaginal test, wherein an ultrasound probe is inserted via the vagina.
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From the ultrasound image, the doctor measures the translucency, or clear space, at the back of the baby's neck.
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To determine the likelihood of your baby's abnormality, you may be asked for your age or date of birth, which will be entered into a computer program for calculation.
An NT scan cannot diagnose Down syndrome or any other chromosome abnormality but can only predict the risk. Consult your doctor about available blood tests. They also can help assess your baby's risk.
As with any prediction, the accuracy rate varies. If you combine an NT scan with blood testing, the screening is about 85% accurate for predicting the risk of Down syndrome. If you don't combine blood testing with the scan, the accuracy rate drops to 75%.
How Much Time is Required for an NT scan?
Typically, the scan lasts for around 30 minutes. The sonographer may request you to wait in the ultrasound room following the scan to review the images.
Sometimes it will be necessary for the specialist to attend the examination to carry out more scans or to look at the images on the screen rather than just the still pictures taken during the scan.
Ultrasound NT Scan Results
The NT scan measures the thickness of the translucent (black) region behind the fetus's neck, representing the fluid in the nuchal fold of the developing baby.
Normal Values
The values considered normal and indicating a lower risk of genetic disorders in the developing baby are given in the following table:
| Pregnancy Duration | NT Measurement |
| 11 weeks | 2.1 mm |
| 13 weeks 6 days | 2.8 mm |
Abnormal Values
Values more than 2.8 mm denote more fluid than usual. The higher the fluid measurement, the higher the risk for genetic disorders like:
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Down Syndrome
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Patau Syndrome
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Edwards Syndrome
Is 3.5 mm NT Normal?
Fetal NT ≥ 3.5 mm indicates invasive testing, often followed by chromosomal microarray. NT ≥ 3.5 mm is a well‐recognized indication for invasive testing as it is a well‐studied ultrasound marker for common and uncommon aneuploidies, genetic syndromes, and structural anomalies.
NT Scan Result Chart
NT scans can only bring results between 11 weeks to 13 weeks or when the baby's crown-rump length is between 45 mm and 84 mm. Before 11 weeks, the scan cannot be done because the size of the fetus is too small.
After 14 weeks, it gets late because excess nuchal fluid may be absorbed in the baby's lymphatic system.
The NT scan can detect about 77% of babies having Down's syndrome. However, it may also give a false-positive result where even if there are meager chances of having the syndrome, the result may show a high probability.
The results may be more accurate if blood tests are combined with an NT scan. These blood tests include hormone levels, free beta-hCG, and PAPP-A protein. Babies having Down's syndrome tend to have high levels of hCG and low levels of PAPP-A.
There is another screening test known as non-invasive prenatal testing, which has nearly 99% accuracy in detection.
The normal thickness of the nuchal fold at 11 weeks is up to 2 mm; at 13 weeks, six days is up to 2.8 mm. Any abnormality in the measurements indicates the risk of Down's Syndrome.
To get a confirmed diagnosis, if there are any abnormalities, another test called amniocentesis is performed.
Other Tests Done with NT Scan
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Double-marker blood test: This test measures the level of the hormone beta-HCG (human chorionic gonadotropin) and pregnancy-associated plasma protein-A (PAPP-A). The levels of HCG and PAPP-A are higher in the child with Down syndrome.
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Non-invasive prenatal test (NIPT): During pregnancy, it is possible to check for cell-free fetal DNA in the mother's blood as early as week 8 through a maternal blood test.
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Chorionic Villus Sampling (CVS): During weeks 11 to 14 of pregnancy, a test called ultrasound-guided placental tissue extraction is done to evaluate the developmental status of the fetus.
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Amniocentesis: Typically performed between weeks 15 and 18. This involves using an ultrasound to guide the extraction of a specific amount of amniotic fluid, which is then analyzed for any potential chromosomal abnormalities in the fetus.
Key Takeaway
An NT scan is a safe, non-invasive test that does not cause any harm to you or your baby. Keep in mind that this first-trimester screening is recommended, but it's optional. Some women skip this test because they don't want to know their risk. If you are experiencing anxiety or concerned about the impact of the results, it is advisable to consult your doctor.
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