Down’s syndrome is suitable as a screening disease: (1) the affected children are severely mentally retarded, the population incidence rate of 1/600-1/800, the onset of random and sporadic; (2) screening after the high-risk group can be prenatal diagnosis through amniocentesis; (3) whether serological screening, ultrasound screening or non-invasive fetal free DNA screening, the method is simple, economic, non-invasive to the fetus; (4 (4) Each birth of a child with chromosomal disorders causes an economic burden of several hundred thousand yuan to society, and the total cost of treating children with chromosomal disorders in China exceeds 2.5 billion RMB annually. Relying on the current medical level and technological means, Down syndrome cannot be cured. Therefore, the only effective way to reduce the birth rate of children with Down’s syndrome is to screen all pregnant women for Down’s syndrome and perform prenatal diagnosis for pregnant women with high risk of screening, that is, to diagnose whether the fetus has Down’s syndrome before it is born, so as to avoid the birth of Down’s children.