Non-invasive DNA is a prenatal screening tool, without prenatal diagnostic indications of pregnant women can be mainly 13, 18, 21 trisomy three tests, there is no need to do non-invasive DNA 100, there are prenatal diagnostic indications more recommended amniocentesis. Non-invasive DNA can detect fetal genes according to the components in the blood to determine whether there is a high risk of the existence of the fetus, but also to further assist in the diagnosis of whether the fetus has congenital diseases, such as checking whether chromosomal disorders, hereditary diseases, and so on, but also check whether there is a trisomy 21, usually three can meet the requirements, there is no need to carry out the 100 items. The non-invasive DNA test is more accurate, less painful, and generally does not pose a risk of miscarriage, but the test is more expensive. Amniocentesis is more recommended for higher accuracy if the mother is of advanced maternal age, or if she has other risk factors, those with indications for prenatal diagnosis i.e. family history of genetics, positive Down’s screen, chromosomal abnormalities, and those who have experienced miscarriage or fetal arrest.