Down screening, also known as Down’s syndrome screening, is the abbreviation for prenatal screening for Down’s syndrome, which is also a prenatal assessment of the risk of Down’s syndrome in the fetus. By checking the relevant indicators in the pregnant woman’s blood, and combining the pregnant woman’s weight, age, gestational week and other factors, the risk of Down’s syndrome in the fetus is comprehensively assessed, and the next arrangement for pregnancy preparation and treatment is decided. Different hospitals and regions have slightly different screening methods due to different conditions and situations, and currently there are mainly the following ways: 1. Early screening: the test is conducted between 11-13 weeks of pregnancy, the pregnant woman’s blood is taken on an empty stomach, and the fetoprotein and free beta-hCG are tested, and the NT value is checked by ultrasound, and the risk assessment of Down’s syndrome screening is conducted by a combination of indicators, and the detection rate can be as high as 85%, which is relatively good. The detection rate can be as high as 85%, which is a relatively good screening program, but it cannot provide the risk of open neural tube defects; 2. Mid-term Down’s syndrome screening: the screening is performed between 15-20 weeks of pregnancy, and the triple screening is commonly used at present, that is, fasting blood is taken to test the concentration of methemoglobin, free estriol and β-hCG, and the comprehensive risk assessment is performed, and the detection rate is about 60%-70%; 3. If the results of early and mid-term Down’s screening are considered to be high or critical risk, or if the pregnant woman has had a previous pregnancy or delivery with chromosomal abnormalities, or if either spouse is a carrier of chromosomal abnormalities, further chromosomal testing can be performed through amniocentesis or non-invasive DNA to clarify whether the fetus has Down’s syndrome or not.