A low noninvasive blood level does not mean that the child is unhealthy. Non-invasive, or non-invasive DNA testing, is a method of fetal chromosome screening during pregnancy. When non-invasive DNA testing is performed, the low concentration of fetal free DNA in the blood is not caused by the child being unhealthy, but is mainly related to the mother, such as excessive blood viscosity of the pregnant woman, insufficient blood collection, or non-compliance with the gestational week, which will lead to the non-invasive blood concentration and make the accuracy of the results less accurate. Non-invasive DNA testing is based on the free DNA fragments of the fetus in the peripheral blood of the pregnant woman, and the extracted DNA is sequenced to determine whether there is any chromosomal abnormality or abnormality in the fetus. If the test results suggest the possibility of fetal chromosomal abnormalities, further amniocentesis may be required. Non-invasive DNA testing should pay attention to the time, usually in 12-26 weeks of pregnancy is appropriate, when the concentration of fetal free DNA fragments in the peripheral blood of pregnant women is higher.