For women who are pregnant with a child, usually around 50 days of pregnancy, an ultrasound is needed to confirm that the pregnancy is intrauterine and that the fetal heart and germ are growing. In the third month of pregnancy, a card will be issued and a full maternity check will be done, and an NT test is usually recommended at this time. Therefore, the best time to have an NT test is within 11-13 weeks of pregnancy, when the nuchal translucency and nasal bone can be clearly seen. As long as the NT value is less than 2.5mm and the nasal bone can be seen clearly, it means that the fetus is growing normally and there is no need to consider any other abnormalities. However, routine Down’s syndrome screening is still required at 16 weeks of pregnancy.