1. Primary screening system: clinical screening, which identifies high-risk or low-risk pregnant women through clinical observation and physical examination of pregnant women and their husbands, taking into account their age, past medical history, past pregnancy and childbearing history, family genetic history, and history of exposure to teratogenic factors. 2. Secondary screening system: Laboratory screening, targeting high-risk pregnant women by testing the pregnant women and/or their husbands for hematological indicators, biochemical markers and biochemical indicators, immunological and microbiological indicators, and genetic indicators. (3) Three-tier screening system: medical imaging screening, which is mainly reflected in the three lines of defense of fetal ultrasound examination: (1) The first line of defense: the first ultrasound examination is conducted from 10 to 14 weeks of gestation, and during this period, the main purpose is to carry out ultrasound examination of genetics, and at the same time, to test for some large structural malformations such as anencephaly and conjoined babies. (2) Second line of defense: ultrasound examination from 18 to 24 weeks, this period is the best time for detecting most structural malformations, during which every mother-to-be undergoes a rigorous systematic and detailed prenatal ultrasound diagnosis. (3) Third line of defense: another ultrasound at 32 weeks, which is able to detect malformations that could not be detected at 18 to 24 weeks or that have not yet appeared.