Prenatal screening is a comprehensive assessment of risk based on maternal age, ultrasound and blood tests. Low risk does not necessarily mean that the disease will not develop, and high risk does not necessarily mean that the disease will develop, but the probability of developing the disease is higher than that of the general population. From the eugenic point of view, it is recommended to do amniocentesis to further clarify the diagnosis, although many Down’s syndrome screening high-risk after amniotic fluid chromosome test or after birth is a normal fetus, but in order to ensure the safety of the best to do the test, so that the pregnant woman can rest assured, otherwise the pregnancy is always tense, is not conducive to the development of the fetus.