Non-invasive DNA is non-invasive prenatal DNA testing, which mainly checks whether the fetus has chromosomal disorders. Non-invasive DNA test is performed by sequencing the free DNA fragments in the peripheral plasma of the mother by using DNA sequencing technology on the venous blood drawn from the pregnant woman. Based on the sequencing results, further analysis of the biological information is carried out, so as to diagnose the genetic information of the fetus, to determine whether it will suffer from the three major chromosomal diseases, and to rule out the existence of abnormalities in the fetus. Currently, there is no effective treatment for chromosomal diseases. Therefore, it is necessary to detect and solve the problem through prenatal testing as early as possible. The advantages of non-invasive DNA testing are that it avoids the risks of infection and fetal miscarriage associated with invasive prenatal testing, has a high detection rate of trisomy 21, 18 and 13, and is applicable to a wide range of gestational weeks (12-24 weeks of pregnancy can be tested). Non-invasive DNA test is mainly applicable to pregnant women who have found abnormal embryonic development in the previous examination, and who are not suitable for invasive prenatal examination voluntarily or physically, in the clinic, non-invasive DNA test is generally chosen, and it can more accurately exclude the possibility of the occurrence of the three major chromosomal disorders.