The Down screening biochemical marker risk refers to the risk of the fetus having Down syndrome, and amniocentesis is also required if the condition needs to be determined. Down screening is used to check for Down syndrome and is usually performed at 10-13+6 weeks of gestation. Its biochemical marker risk is mainly used to indicate the probability of a fetus having Down syndrome, but it does not necessarily mean that it is a Down’s fetus. The biochemical marker risk threshold is between 1/1000 and 1/270, and if the value is >1/270, it indicates a high risk. Early screening for Down syndrome has a detection rate of 85% and a false-positive rate of 5%; midterm screening for Down syndrome has a detection rate of 60-75% and a false-positive rate of 5%. Amniocentesis is also required to confirm whether the fetus has a chromosomal problem.