Nuchal translucency is a fluid-filled space behind the neck of a fetus. Nuchal translucency scan is commonly known as NT scan, and it is done to check the size of Nuchal translucency during 11 to 13 weeks of pregnancy.The test is used to screen for Down Syndrome or any other chromosomal abnormalities.
Normally all developing fetus have fluid behind their neck. But there is an increased amount of the fluid in developing fetuses with Down Syndrome. During the 11 to 13 weeks of pregnancy, some of the non-chromosomal conditions, such as congenital heart disease, abdominal wall defects, neural tube defects and other conditions can also be detected.
You will be undergoing an abdominal ultrasound. Sometimes, you will be referred to a transvaginal test. No matter what your age is, you will be referred to an NT scan by your doctor. The scan is normally done-
When Will I Have A Nuchal Scan?
You can undergo an NT scan only in certain stages of your pregnancy. Normally, an NT scan is done if you’re between 11 weeks and 13 weeks of pregnancy. It is recommended to undergo a nuchal translucency scan at 12 weeks. During 11 weeks of pregnancy, you can’t undergo a nuchal scan at that stage, and your scan will be postponed. Since the nuchal fluid will be absorbed by the lymphatic system, you can’t undergo the scan if you’re 14 weeks pregnant. The NT scan results will be inaccurate.
Why Do You Need To Undergo A Nuchal Scan?
Expectant mothers should undergo a nuchal translucency scan to determine whether or not there are chances of chromosomal abnormality such as Down Syndrome. An NT scan is just a part of the detailed scan that you undergo during your first trimester.
If you’re older, then you have more chances of giving birth to a baby having Down Syndrome. By undergoing a screening test, it can be determined whether or not a baby has Down Syndrome. But there is no certainty with an NT scan. Therefore, after undergoing amniocentesis or chorionic villus sampling, it can be confirmed whether your baby has Down Syndrome or not. Not only the NT scan results are considered in the screening test, your age and blood test results and other factors are also taken into consideration. You can determine the abnormality so that you can go ahead with a diagnostic test.
Nuchal Translucency Scan Procedure
For an NT scan, you don’t need any preparations. The procedure takes less than 30 minutes. Sometimes your doctor will ask you to drink water prior to the scan. The images will be easier to comprehend if you undergo the scan with a full bladder.
During the procedure, you will be asked to lie down on a table. A technician will apply a water-based gel on your stomach and move the ultrasound device through your stomach.
The ultrasound transducer transmits the ultrasound waves that are reflected back to the ultrasound machine, producing images. You will be able to view the images on an ultrasound screen.
Sometimes, the doctor will ask you to undergo a transvaginal scan if your uterus has a backward tilt,(also known as the retroverted uterus) or if you are obese. To undergo a transvaginal scan, you need to empty your bladder. The scan is completely safe for the baby and mother.
Your doctor can confirm the date of pregnancy after measuring the baby from head to spine. Thereafter, your doctor measures the width of the fluid. Below the skin, the fluid appears as black while on the skin appears as a white line.
During the scan, the doctor can rule out certain abnormalities related to the skull, stomach, abdominal wall, and urinary bladder.
Sometimes your doctor will ask you to undergo an anomaly scan or TIFFA scan between the 18 to 20 weeks of pregnancy, where more features of the baby will be visible.
Through the screening, the heart rate, foetus structure, number of foetuses, size of the foetus etc. can be determined.
Sometimes, the results will be available on the same day when you have undergone the scan, and the doctor will explain to you the results.
What Does The Nuchal Translucency Levels Indicate?
Nuchal Translucency level of less than 3.5 mm is normal. Down syndrome can be ruled out if the measurement is between 2.5mm and 3.5mm. In this case, only 1 out of 10 babies have Down Syndrome. With an increase of NT levels, there is more possibility for chromosomal abnormalities.
If the baby has an NT level of 6mm, there is a higher possibility of chromosomal abnormalities. This rarely occurs in babies.
What Do The Results Indicate?
The results of the NT scan indicate whether or not the developing fetus has Down Syndrome. Up to 75% of the results are accurate.
There are two chances for a baby to have Down Syndrome-
1:30- It means that out of 30 pregnant women who have similar results, one baby has Down Syndrome, while the rest 29 babies won’t have Down Syndrome.
1:4000- It means that out of 4000 pregnant women who have similar results, one baby has Down Syndrome while the rest 3999 babies won’t have Down Syndrome.
If the second number is high, for instance 4000 in 1:4000, there will be lower risk.
The results can be classified as low risk and high risk. In such cases, a cut off of 1 in 350 is used.
1:30 is considered as high risk because it is riskier than 1:350
1:4000 is considered as low risk because it is less risky than 1:350
Out of 20 women who undergo an NT scan in pregnancy, 19 women have normal results.
How To Diagnose An Abnormality?
There are two procedures to diagnose an abnormality.
Amniocentesis- A fluid sample is taken from the amniotic sac.
Chorionic Villus sampling- A placental tissue sample is taken to diagnose chromosomal abnormalities.
But there is a slight risk of miscarriage for both amniocentesis and chorionic villus sampling.
Benefits Of NT Scan
You can determine the chance of Down Syndrome or other chromosomal abnormalities during the early stage of your pregnancy itself. This is the main benefit of an NT scan. Thereafter, you get a chance to discuss the test results with the doctor. NT scan cost varies between Rs 800 to Rs 1200. Suppose if the screening indicates a risk, you have to confirm the results by undergoing other tests such as chorion villus sampling or amniocentesis. Therefore, you can make a decision on whether to keep the baby or not.
An NT scan is considered as safe. It does not cause any harm to your baby. But make sure that you undergo an NT scan only in the first trimester. The reason why an NT scan should be conducted in the first trimester is that the space behind the neck can disappear by the 15th week of pregnancy. Discuss an NT scan, its procedure and the possible results, with your doctor, before undergoing the scan.