Nuchal translucency (NT) scan is a common ultrasound test that is done to measure the amount of fluid behind the baby’s neck, called the nuchal fold, in the first trimester of pregnancy. This test assesses if a baby is at risk for genetic conditions by measuring the size of the clear tissue, called the nuchal translucency, at the back of the baby’s neck. Excessive clear space at the back of the neck indicates Down syndrome, or a chromosome abnormality like Patau syndrome or Edwards' syndrome. The advanced NT measurement may also indicate an increased risk for congenital heart conditions and also screens for basic anatomical structures of the unborn baby (foetus). The NT scan is performed when the baby is between 11-13 weeks of gestation and measures 45-84 millimetres in size from the crown to the rump. Read on to learn more about what an NT scan is during pregnancy.
What is nuchal translucency in pregnancy?
A nuchal translucency (NT) test is a type of ultrasound screening test that is performed in the first trimester of pregnancy because the clear space in the back of a developing baby’s neck disappears by 15 weeks. At 11 weeks of pregnancy, the skin folds at the back of the neck measure up to 2 mm and at 13 weeks it grows up to 2.8 mm in size. The results from this screening test do not offer 100% surety of whether the baby will have a chromosomal abnormality or not. If the result shows a high risk for the developing foetus, then a doctor may recommend a diagnostic procedure like chorionic villus sampling, which provides a definitive result.
So, what is an NT scan during pregnancy going to result in? The results are usually reported as either of the two risks:
- Low risk: The result is said to be low risk when fewer than 1 in 300 tests indicates a risk of chromosomal abnormality
- High risk: The result is said to be high risk when more than 1 in 300 indicates a risk of abnormality.
The nuchal translucency scan results can be combined with a blood test performed within 10 to 12 weeks of pregnancy, to form a ‘combined first-trimester screen’, or CFTS that provides a more accurate estimate of the risk.