Both Down screening and non-invasive DNA are used to test for the chance of developing Down syndrome. There are no definitive studies that show that the two are interchangeable. Down syndrome, also known as syndrome 21, is due to an extra chromosome on the 21st pair of chromosomes, called trisomy. Down’s babies, the most common cause of mental retardation in babies. Non-invasive prenatal DNA testing, also known as non-invasive fetal chromosome aneuploidy testing, is the most widely used technology, requiring only venous blood from the pregnant woman, with an accuracy rate of more than 90%. Non-invasive DNA prenatal testing can avoid the risk of miscarriage and infection associated with invasive diagnosis. The Down’s syndrome screening test is actually an abbreviation for Down’s syndrome prenatal screening test. The test is performed by testing the blood of the pregnant woman to determine the concentration of alpha-fetoprotein, chorionic gonadotropin and free estriol, as well as the age, weight and days of menopause of the pregnant woman to determine the risk of congenital dysmorphism and neural tube defects in the fetus. The detection rate of Down’s syndrome is only 60% to 70%, and the accuracy rate is only 50%. However, Down screening is cheaper, while non-invasive tests are more expensive and not covered by medical insurance in many hospitals. If a pregnant woman is financially well off, she can have a non-invasive DNA test directly. If the screening test is high or critical risk, a non-invasive DNA test is also required.