Non-invasive DNA can detect three common diseases, trisomy 21, trisomy 18 and trisomy 13, such as non-invasive DNA trisomy 21 high risk, the chance of normal amniocentesis is about 1%. Non-invasive DNA, also known as fetal chromosome aneuploidy non-invasive genetic testing, is a common means of screening for chromosomal abnormalities in mid-pregnancy, with an accuracy rate of about 99%. Non-invasive DNA is only a means of screening, and can not be used as the final result, such as suggesting a high risk, need to carry out prenatal diagnosis, a clear diagnosis, and non-invasive DNA high-risk, the chances of a normal amniocentesis is about 1%. Compared with Down’s screening, non-invasive DNA is more accurate, but still has limitations, for fetal developmental abnormalities, pregnant women older than 35 years old, couples with a family history of genetic diseases, should be under the guidance of the obstetrician to choose the appropriate screening method.