NT test, also known as posterior nuchal translucency scan, is the use of ultrasound to determine whether there is any developmental abnormality in the fetus. It is mainly used to assess whether the fetus is suffering from Down’s syndrome, with a high rate of accuracy, and does not require the drawing of blood. If blood is drawn during the NT test, the test may be combined with a Down’s syndrome screening test for a definitive diagnosis of the presence of Down’s syndrome. It is currently recommended that Down’s syndrome screening be done twice, including early and mid-trimester screening, called combined early and mid-trimester sequential screening, which has a detection rate of up to 85%. Early trimester screening is performed by combining the NT value with serologic testing to detect risk values for trisomy 21 as well as trisomy 18. If the early trimester screening is low risk, it is recommended to continue with mid-trimester screening, and if it is a critical or high risk, it is not necessary to continue with mid-trimester screening, and non-invasive DNA or amniocentesis testing is recommended. In addition, the NT test is best performed at the stage of (11-13) weeks + 6 days of pregnancy, while after 12 weeks pregnant women need to be documented, therefore, blood sampling during the NT test may also be required for documentation, and the items needed to be checked include height, weight, abdominal circumference, blood test, liver and kidney function, blood glucose, etc., and blood sampling needs to be performed on an empty stomach.