One tube of blood is usually drawn for Down screening of pregnant women. It is an important screening program during pregnancy. It is an important maternity test during pregnancy and is divided into early pregnancy screening and mid-pregnancy screening.1. Early pregnancy screening: usually performed at 11-13 weeks +6, mainly detecting the concentration of two serum markers, serum pregnancy-related protein-A, human chorionic gonadotropin or free β-hCG, and ultrasound measurement of fetal nuchal translucency layer (NT) thickness, combined with maternal age, gestational week and weight and other parameters to calculate the risk of fetus suffering from The risk factor for trisomy 21 and trisomy 18 is calculated by combining maternal age, gestational week and weight. 2. In general, it is advisable to go for Down’s syndrome screening on an empty stomach in order to avoid any food disturbances that may affect the accuracy of the results. Provide accurate information on the age, weight and week of gestation of the pregnant woman at the time of consultation. Since the gestational week has a significant impact on the accuracy of the test results, careful verification of the gestational week is needed, either based on early pregnancy or the NT ultrasound gestational week between 11 and 14 weeks.