What is USG OBST NT ?

There are a number of tests and scans available to you during your pregnancy. The nuchal translucency scan is an ultrasound that may detect the risk of a number of chromosomal abnormalities.

What is a nuchal translucency scan?

A nuchal translucency scan is part of the ultrasound scan that most pregnant women have at around 12 weeks of pregnancy. If you decide to have the scan, the health professional performing the ultrasound will measure your baby's nuchal translucency (a fluid-filled space at the back of your baby's neck).

The results of a nuchal translucency scan may tell you if your baby has a high or low risk of a chromosomal abnormality. Examples of chromosomal abnormalities include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), or trisomy 13 (Patau syndrome).

What does a nuchal translucency scan look for?

Increased thickness of the nuchal translucency might indicate a chromosomal abnormality, but it doesn't tell you that your baby definitely has, or doesn't have, an abnormality. The results will tell you if your baby is at high risk or low risk of chromosomal abnormality in comparison to the general population.

How is a nuchal translucency scan performed and when?

The nuchal translucency scan is done between 11 and 14 weeks of pregnancy. It might need to be done alone, or it might be able to be done while you’re having your dating scan.

Usually, the scan is done through your abdomen but occasionally the nuchal translucency can only be seen by inserting a probe into the vagina.

You might also be offered a blood test around this time. Your doctor can look at the results of the combined test (blood test and nuchal translucency scan) to get a more accurate picture of the risk of a chromosomal abnormality.

What happens if my baby is in the high-risk category?

The results of the nuchal translucency scan will not be used alone to calculate the risk of a chromosomal abnormality. All your first-trimester screening is combined to calculate your risk. The calculation is based on the mother’s age, the nuchal translucency measurement of your baby, the gestational age of the baby, blood tests, and the baby’s nasal bone.

If you have a risk of 1 in 300 or greater (e.g. 1 in 150) you are considered to be in the "increased risk" category.

Even if you are classified as high risk, remember your baby probably doesn’t have a chromosomal abnormality. You may be referred to a genetic counselor. They will discuss your options and help you to decide if you would like to have a more invasive diagnostic test, such as chorionic villus sampling (CVS) or amniocentesis. These diagnostic tests can tell you definitively if your baby has a chromosomal abnormality or not. Tests such as CVS and amniocentesis carry a small risk of miscarriage.

Do I have to have the test?

No, it is your decision.

You might choose to have a nuchal translucency scan or you may choose to go straight to one of the more invasive diagnostic tests instead to get a definitive answer. You can have chorionic villus sampling from 11 weeks of pregnancy, or you can have an amniocentesis from 15 weeks of pregnancy.