Through the course of your pregnancy, you will be asked to take a number of tests and at times a few scans. In some cases, you may be asked to take a nuchal translucency (NT) scan. An NT scan is an ultrasound that helps to detect any chromosomal abnormalities in the growing baby.
So, what exactly is nuchal translucency?
Nuchal translucency (NT) is nothing but a collection of fluid under the skin present at the back of your little one’s neck (the nuchal fold). An NT scan measures this fluid thickness in an ultrasound and mainly helps in assessing the risk of Down’s syndrome ( the more the fluid level than normal, then it could be a positive indicator).
What is a nuchal translucency scan?
A nuchal translucency scan is part of the ultrasound scan done in the first trimester (around 12 weeks of pregnancy). If you have been asked to do an NT scan, then the ultrasound will measure the size of the nuchal fold (at the back of the baby’s neck).
The results of a nuchal translucency scan tell if the baby has a high or low risk of a chromosomal abnormality. This includes Down’s syndrome (trisomy 21), Edward’s syndrome (trisomy 18) or Patau syndrome (trisomy 13).
How do you perform a nuchal translucency?
In most cases, the scan is done through your abdomen but in some cases, the nuchal translucency may require the probe to be inserted vaginally, so speaking to your doctor would be best!
Round about the same time, a blood test would be done. Your doctor then can get a more comprehensive picture based on the combined tests i.e., the blood test and the NT scan.
What can a nuchal translucency indicate?
By doing an NT scan, you will get to know if your baby is in the high-risk category for having any chromosomal disorders. It should be kept in mind that, the results of the nuchal translucency scan alone cannot calculate the baby’s risk to have a chromosomal abnormality. The test indicated by your doctor during your first trimester (screening tests) all together help calculate risk.
The calculation is done by taking into consideration the following parameters:
Of the mother:
- The mother’s age
- Blood test findings
Of the baby:
- The nuchal translucency measurement
- The gestational age blood tests
- The nasal bone
The values are interpreted as follows:
- Low Risk: the risk is lesser than 1 in 1000
- Intermediate Risk: the risk lies between 1 in 50 and 1 in 1000
- High Risk: the risk is greater than 1 in 50
Even if you are classified as high risk, remember your baby probably may still not have a chromosomal abnormality. You will be asked to do some more confirmatory tests and also be referred to a genetic counselor. Speaking to your doctor will help you get clarity on the need of getting a more invasive diagnostic test done like such as chorionic villus sampling (CVS) or amniocentesis. These diagnostic tests give a definitive result (if your baby has a chromosomal abnormality or not) but due to their invasive nature, they run the risk of causing a miscarriage.
Is a nuchal scan mandatory?
Depending on what your doctor says, you can make an informed decision. You can choose to have an NT scan or depending on what options your doctor presents you with, you can choose to go ahead straight with one of the more invasive diagnostic tests for a more definitive answer when in doubt. Advance tests options include chorionic villus sampling (week 11 onwards) or amniocentesis (week 15 onwards). Or you can decide not to have any – it is purely your choice. But we still request you to take a decision taking into account your family and doctor’s opinion.