Pregnant women can be screened for malformations at 12 weeks, 13-16 weeks, 16-20 weeks, and 20-28 weeks through non-invasive DNA, Down’s screening, amniocentesis, and 4D ultrasound.1. 12 weeks of gestation: non-invasive DNA can be used to detect free fetal DNA in the pregnant woman’s bloodstream, and blood and blood can be drawn, and by means of gene sequencing, to determine whether the fetus is at risk for Down’s syndrome.2. Gestation 13-16 weeks: Down’s syndrome screening can be carried out to check the nuchal translucency, nasal bone dysplasia, cardiovascular malformations, alpha-fetoprotein, free estriol and so on, to determine whether the fetus is abnormal or not; chromosomally abnormal fetuses, after delivery, are often accompanied by special facial features, such as sluggishness, upward slanting of the outer side of the eyes, backward intelligence, growth retardation, developmental deformities, and susceptibility to diseases, etc.; 3. 16-20 weeks of gestation: advanced age of more than 34 years old Pregnant women, pregnant women with Down’s syndrome at home, pregnant women who have already given birth to a child with Down’s syndrome, and those who are at high risk for blood sampling, need to undergo amniocentesis to further check whether there are chromosomal abnormalities, and to determine whether the baby is malformed after about 7 days of chromosome peening, such as Down’s syndrome, beta-marine anemia, hemophilia, spina bifida, congenital nephropathy, esophageal or intestinal atresia, and complete absence of the brain, etc.; 4, 20 weeks of pregnancy -28 weeks: through four-dimensional ultrasound, it can dynamically observe the fetus in the uterus, including the development of the fetal body surface and internal organs, and can check out cleft lip and palate, abnormal development of the central nervous system, malformation of internal organs, congenital heart disease and so on. Therefore, 16-28 weeks of a woman’s pregnancy is a critical period for fetal exclusion tests, and pregnant women are advised to do regular prenatal checkups to ensure the normal development of the fetus.