Down syndrome, also known as trisomy 21, is a congenital disorder caused by an extra chromosome 21. According to the Chinese Eugenics Association, on average, there is one case of Down syndrome every 20 minutes, and there are about 800,000 to 1.2 million “Down babies” born every year. People with Down’s syndrome have special facial features, such as upturned corners of the outer eyes of the eyes, a tongue that often protrudes outward, and a hand that passes through the hand. The vast majority of patients are severely mentally retarded and have multiple organ abnormalities, such as congenital heart disease, leukemia, and digestive tract malformations. The birth of a child with Down’s syndrome brings a heavy economic and psychological burden to the family and society, and there is no effective medical treatment program for the born children. At present, the only effective and feasible measure is to carry out prenatal screening for Down’s syndrome (Down screening).