The most appropriate gestational week for NT is 11~13+6 weeks, and it needs to be performed under the supervision of a doctor. NT refers to the thickness of fetal nuchal translucency, early pregnancy through the ultrasound examination to determine the value of NT, can be a preliminary screening of the risk of chromosomal abnormalities in the fetus, need to follow the doctor’s advice at 11~13+6 weeks of pregnancy when the examination is the most appropriate, and should be operated by a professional physician, the normal value of <2.5mm. When the NT test indicates an abnormality, it only indicates an increased risk of chromosomal abnormality in the fetus, but it does not lead to a definite diagnosis, and further prenatal counseling and prenatal diagnosis are needed to make a definite diagnosis under the guidance of a doctor. Meanwhile, a negative result does not mean that the development of the fetus is normal, and needs to be combined with the later Down's syndrome screening, systematic ultrasound examination and other screening tests to clarify. During pregnancy, you should follow the doctor's instructions and go to the hospital for timely checkups and treatments if you feel unwell.