Nt is also known as NT, the scientific name of NT is the thickness of the posterior nuchal translucency. It is recommended that pregnant women check the NT at 11 to 13 +⁶ weeks of pregnancy, the normal value of NT is 0 to 3mm, the value of the check out is normal, it means that the development of the fetus is relatively good, if the value of the check out is more than the normal range, the fetus may suffer from chromosomal abnormality disease. When the NT is 3mm, the risk of Down’s syndrome increases 3 times, when it is 4mm, it increases 18 times, and when it is 5mm, it increases 28 times. After pregnancy, it is recommended to go to the hospital for the NT test at the prescribed time, and when the test result is abnormal, further diagnosis and treatment should be carried out according to the doctor’s guidance and advice.