NT Scan : Purpose, Risks, Procedure and Results

Lab Test and Medical Investigation

Overview

Antenatal checks and prenatal screening are crucial during pregnancy at regular intervals. Antenatal checks for the expecting mother can identify problems with her health, including anaemia, hypertension or gestational diabetes. The prenatal screening evaluates the health of their developing baby and helps identify chromosomal abnormalities.

Women undergo pregnancy screenings during the first, second, and third trimesters. The first-trimester screening of the fetus provides early information about the baby’s health and identifies chromosomal abnormalities.

The nuchal translucency (NT) test is one of the many tests a doctor recommends for a pregnant woman. Doctors schedule the NT scan between weeks 11 and 13 of the pregnancy to check for possible abnormalities.

This blog is a comprehensive guide to NT scan, its purpose, risks, the procedure, and results.

What is an NT scan?

An NT scan (also known as the nuchal translucency test) uses ultrasound to assess the developing baby’s risk of having Down syndrome and other chromosomal abnormalities. The nuchal translucency test measures the thickness of nuchal fold. This is a tissue area at the back of an unborn baby’s neck. Measuring this thickness helps determine the baby’s risk for Down syndrome and other genetic problems.

What is the purpose of an NT scan?

Doctors recommend the NT scan during the first trimester of pregnancy.

It is usually part of the combined first-trimester screening which includes an ultrasound and blood test . The ultrasound will confirm duration of the pregnancy . Additionally, a measurement of the fluid beneath the skin along the back of the neck of the baby, called the nuchal translucency (NT), is be taken. The ultrasound will also try to measure if your baby’s nasal bone is present.

A maternal blood sample is used to measure levels of free beta-human chorionic gonadotropin (hCG), alpa-fetoprotein (AFP) and pregnancy-associated plasma protein-A (PAPP-A) that is found in the blood of all pregnant women. In certain pregnancies, when the baby is diagnosed with Down syndrome, trisomy 18 or trisomy 13 there is extra fluid behind the neck of the baby, and/or the hCG, AFP and PAPP-A results are higher or lower than the average. Combining the age-related risk with the NT measurement, nasal bone data and bloodwork provides one risk figure for Down syndrome and one risk figure for trisomy 18 or trisomy 13.

Down syndrome people have an extra chromosome 21. Down syndrome is not curable and leads to developmental delays. Both Patau syndrome and Edwards syndrome are rare and usually fatal. In most cases, babies with Patau syndrome and Edwards syndrome die within the first year of their life.

Combined first-trimester check up is not a diagnostic test. This means it cannot tell whether your baby has trisomy 13, trisomy 18, or Down syndrome. Instead, the screening offers a probability that the baby may have trisomy 13, trisomy 18, or Down syndrome.

When does a doctor schedule an NT scan during pregnancy?

It is crucial to complete the NT scan within 11-14 weeks of pregnancy as the clear space at the back of the developing baby’s neck may disappear.

How does an NT scan work?

The doctor will place a transducer (small plastic device that sends & receives sound waves) over your abdomen. The reflected sound waves will be converted digitally into images on the monitor. Your doctor or technician will use these images to determine the size of the clear space in the tissue at the back of your baby’s neck.

An expectant mother should remember that an NT scan cannot diagnose Down syndrome or any other chromosome abnormality but can only predict the risk..

With any prediction, the accuracy varies. However, the accuracy of predicting the risk of Down Syndrome is about 85 per cent when a pregnant woman undergoes both NT scans with a blood test. The accuracy rate drops to 75 per cent when expectant mothers do not combine a blood test with the scan.

Are there any risks of an NT scan?

NT scan is known to have no risks as ultrasound uses sound waves to obtain images. It does not use any radiation. Women can undergo as many scans as they require without risk to them or the baby.

What do NT scan results mean?

Normal NT Scan Results

A pregnant woman gets a normal result when there is a normal thickness of the fluid in the back of the baby’s neck during the ultrasound. The result means that the baby is unlikely to have Down syndrome or some other genetic disorder. Nuchal translucency measurement increases with gestational age, the period between conception and birth. The higher the measurement compared to babies of the same gestational age, the higher the risk for genetic disorders. The following measurements mean low risk for genetic diseases:

at 11 weeks – up till 2 mm
at 13 weeks and six days – up till 2.8 mm

Abnormal NT Scan Results

There is a higher risk for Down syndrome, trisomy 13, trisomy 18, Turner syndrome, and congenital heart disease when the results show more fluid than normal in the back of the baby’s neck. However, whether the baby has Down syndrome or another genetic disorder is unclear. When the results are abnormal, doctors recommend other tests called amniocentesis. The doctor draws a small amount of amniotic fluid from the uterus for testing.

Another option is chorionic villus sampling, a form of prenatal diagnosis in which the sample of the women’s placental tissue sample is removed and tested for chromosome abnormalities and genetic problems. There is a minor risk of miscarriage with both tests.

Conclusion

An NT scan is a safe, non-invasive test that does not cause any harm to women or their babies. The patient must remember that this is a first-trimester screening that doctors recommend, but the test is optional. Some women skip this test since they don’t want to know about their risk. Expecting mothers should discuss with the doctor if the patient is experiencing anxiety or are worried about how the results may affect them.

Frequently Asked Questions (FAQs)

1. How do women prepare for this test?

Women must have a full bladder to gain the best ultrasound picture. Before the test, the patient must drink 2 to 3 glasses of water an hour. The ultrasound procedure requires access to the lower abdomen, so women must make sure that they wear comfortable clothing.

2. How does the test feel for women?

Women may have some discomfort from pressure on their bladder during the ultrasound. The patient will not feel the ultrasound waves. The gel that is used over the abdomen can feel slightly cold and wet during the test.