When doing the Down screening, it is generally recommended that pregnant women go to the hospital early in the morning on an empty stomach to have their blood drawn, and they also need to provide the date of their last menstrual period, the week of pregnancy, the weight of the pregnant woman, and the results of previous ultrasound examinations. Down’s syndrome screening is a method of screening for Down’s syndrome, which generally involves testing the blood of pregnant women to determine the probability of the fetus having a chromosomal disorder through serologic indicators. Generally, Down’s syndrome screening is performed around the 14th to 20th week of pregnancy, and requires a previous ultrasound examination of the pregnant woman, as well as her last menstrual period, the gestational week of her pregnancy, and her weight and age to calculate the risk factor for the occurrence of congenital defects. If the pregnant woman’s menstrual period is inaccurate, an ultrasound is also needed to comprehensively analyze the risk level, if the screening is only low-risk, then there is no need to do further testing, if the screening found that there is a critical risk, or high-risk situations, then it is necessary to carry out the next step of the non-invasive DNA or amniocentesis examination. The Down’s syndrome is only a risk test and not a diagnostic tool, so it can only represent the probability of the disease and cannot be used as a final diagnosis.