Down’s syndrome screening is a prenatal screening test to check whether a fetus has Down’s syndrome. Early pregnancy screening is done at 11 to 13+6 weeks of gestation when an ultrasound NT test is performed, and mid-pregnancy screening is done at 16 to 20+6 weeks of gestation when a venous blood test is drawn. Down’s syndrome is a chromosomal disorder that causes severe birth defects in fetuses after birth, which can be characterized by special facial features (wide eye spacing, low nasal root, small eye fissure, lateral upward slanting of the eyes, and open mouth), stunted stature, mental retardation, lack of self-care ability, lack of fertility, and congenital heart disease and leukemia. A child with Down syndrome will bring serious financial burden and mental stress to the family of the affected child, therefore, it is necessary to conduct prenatal screening. The timing of Down’s syndrome screening is divided into early and mid-pregnancy. Early pregnancy screening can be performed between 11 and 13+6 weeks of pregnancy; mid-pregnancy screening can be performed between 16 and 20+6 weeks of pregnancy. The sensitivity of screening varies depending on the gestation period, the age and physical condition of the pregnant woman. Pregnant women who are over 35 years old, have a family history of Down’s syndrome and a history of viral infection are more likely to be found to be at high risk in early screening, and it is recommended that screening be performed in early pregnancy to achieve early detection and early response; pregnant women who have a history of habitual abortion and take teratogenic drugs are more likely to be found to have Down’s syndrome in mid-pregnancy screening. The risk of Down’s syndrome is more likely to be detected in midtrimester screening. In summary, Down’s syndrome screening can be performed between 11 and 13+6 weeks of pregnancy or between 16 and 20+6 weeks of pregnancy. Pregnant women of advanced age, with family history and history of viral infection are recommended to have Down’s syndrome screening in early pregnancy.