Down screening, also known as Down’s syndrome screening, is short for prenatal screening for Down’s syndrome, which mainly screens fetuses for congenital stupidity, neural tube defects and other disorders, and is now one of the mandatory prenatal checkups. Early Down’s syndrome screening is done on an empty stomach at around 12 weeks of pregnancy. Mid-term Down’s syndrome screening is usually chosen, and blood is drawn on an empty stomach during the period of 15 weeks to 20 weeks and 6 days more, that is, before 21 weeks of pregnancy, mainly to check the values of alpha-fetoprotein, HCG, and so on. The blood is drawn on an empty stomach before the 21st week of pregnancy and the values of alpha-fetoprotein and HCG are checked, and the chances of the fetus having Down syndrome are calculated by taking into account the number of weeks of pregnancy, the weight of the pregnant woman and the size of the fetus. If there is a high chance of having an abnormal fetus, further non-invasive DNA testing or amniocentesis is required. Down’s syndrome screening is only a form of prenatal screening, not a definitive diagnosis. If a pregnant woman’s Down’s syndrome screening is a high-risk result, or if she is herself an older woman, she will need to undergo an aggressive amniocentesis test, and if the result is abnormal, the pregnancy usually cannot continue.