What is NT scan?

NT means Nuchal Translucency. There is a collection of fluid at the back of the neck of baby which is called as nuchal fold, which is part of normal development of the baby. The nuchal fold look translucent in the ultrasound image hence called Nuchal translucency.

NT scan is done between 11 to 13 weeks.

What does increased NT means?

Increased NT means increase in the thickness of the nuchal fold as compared to other babies of same length.

What’s the cause of increased NT?

Increased NT is not always abnormal. In most of the cases increased NT resolves and babies are born perfectly healthy. However increased NT is associated with group of conditions and there may not be single cause for increase in the fluid

Increased NT is associated with

Trisomy 21 (Down’s syndrome), Trisomy18 (Edward’s syndrome), Trisomy13 (Patau syndrome), etc.

Genetic syndromes

Congenital cardiac abnormalities

Increased risk of miscarriage

What next if the NT thickness is increased?

To assess the risk of having chromosomal abnormality in the fetus following tests can be done

• Invasive testing like chorionic villous sampling or amniocentesis which are the confirmatory tests to know about the presence of chromosomal abnormality on the fetus.
• Noninvasive or maternal cell free DNA, done on maternal blood. The detection rate by this test is 99%. If the test is negative then it is very unlikely that the baby is having any chromosomal abnormality. But if the test is positive then it has to be confirmed by invasive testing.
• First trimester quadruple test which measures four hormones in maternal blood. It’s detection rate by this test is about 85%.
• Sequential screening- This is combined first trimester test (NT + first trimester quadruple test) done at 11 to 13 weeks and second trimester quadruple test done at 15 to 16 weeks along with anomaly scat at 18 to 20 weeks. The detection rate by this test is around 90 % but the positive result has to be confirmed by invasive testing.