The NT is the thickness of the posterior nuchal translucency layer of the fetus. During early pregnancy, the fetus will have a thin transparent layer like a water sac at the back of the neck due to some metabolism in the fetus, and by monitoring its thickness, the ultrasound doctor can initially determine whether the fetus has any metabolic abnormalities. Generally, the normal value of NT is below 2.5mm at 10-13 weeks. If the NT thickness exceeds 2.5mm, the ultrasound doctor, including the obstetrician, will be on the alert and will highly suspect that the child has Down syndrome, which is commonly known as congenital stupidity, and we cannot conclude that the child is a Down’s child based on the NT thickness alone. We also need to diagnose whether the child is a Down’s child through other tests in the middle of pregnancy, including Down’s screening, non-invasive DNA testing, and amniocentesis if necessary.