The best time for an NT exam is between 11 and 14 weeks of pregnancy. NT, or nuchal translucency, is the thickness of subcutaneous fluid accumulation in the back of the fetal neck in early pregnancy, which appears as a characteristic echo-less area on ultrasound. NT examination before 11 weeks is technically difficult to perform because the fetus is still too small. after 14 weeks, the subcutaneous fluid accumulation may be absorbed by the developing lymphatic system, making it impossible to obtain accurate test data. Therefore the best time for an NT test is between 11 and 14 weeks of pregnancy. An NT examination between 11 and 14 weeks of pregnancy is usually able to accurately rule out the presence of chromosomal abnormalities and underdevelopment of the cardiovascular system, as well as clarify the health status of the fetus. A normal NT value of <2.5mm and an NT value of >2.5mm suggests that the fetus may be at risk for chromosomal abnormalities or Down’s syndrome, and the higher the NT value, the greater the degree of danger. During pregnancy, we must do a good job of obstetric examination, if abnormalities are found, consult a doctor in a timely manner, improve the relevant examination and then targeted treatment.