Down’s screening is currently recommended twice, early and midtrimester screening, called combined early and midtrimester sequential screening, with a detection rate of up to 85%. In contrast, traditional Down’s syndrome screening is only done for mid-trimester screening, with a detection rate of 60%-70% and a high rate of false positives and false negatives. Combined screening is now used as routine screening, but there are hospitals that have not yet performed early screening. The specific practice is as follows,. The NT value is measured by ultrasound at 11-13+6 weeks, venous fasting blood is drawn, NT value combined with maternal serology for early screening, if early screening is low risk, it is recommended to continue midtrimester screening, if it is critical risk or high risk, midtrimester screening is no longer performed, non-invasive DNA or amniocentesis is recommended, midtrimester screening is 15-20+6 weeks, fasting maternal The midtrimester screening is 15-20+6 weeks, fasting blood is taken from the pregnant woman, and the results of the early screening are combined and the report is consolidated, so that the detection rate is higher.