Down screening generally refers to the prenatal screening test for Down syndrome, and after a normal passing of the Down screening test, there is generally no need for a non-invasive test. Down screening and non-invasive DNA is a prenatal screening means, usually in the 16-17 weeks of pregnancy, if the pregnant woman in the Down screening is all normal, and in the ultrasound examination, NT examination also does not have any problem, generally do not need to do non-invasive test. Down’s syndrome screening generally includes early Down’s syndrome screening and mid-term Down’s syndrome screening. Early Down’s syndrome screening mainly uses NT ultrasound to determine the thickness of the fetal nuchal translucency, and then combines with serologic examination. The mid-term Down screening is done by drawing blood and then calculating the risk of developing the disease by taking into account the age, gestational week and weight of the pregnant woman. If the Down’s syndrome test is successful, it usually indicates that the risk of the fetus having Down’s syndrome is relatively low, and in the absence of other abnormalities, no further non-invasive DNA is needed. if the results of the Down’s syndrome test indicate a high risk, further non-invasive or amniocentesis should be considered. In addition, Down’s syndrome screening is not a diagnostic test, a normal Down’s syndrome screening just means that the fetus will have a smaller probability of Down’s syndrome, but it is not necessarily normal, for pregnant women with a family history of the disease should be under the guidance of the doctor to carry out further examination.