Pregnant women can be screened for abnormalities at 12 weeks, 13-16 weeks, 16-20 weeks and 20-28 weeks through non-invasive DNA, Down’s syndrome screening, amniocentesis and 4D ultrasound. 1. 12 weeks of pregnancy: non-invasive DNA can be used to detect free fetal DNA in the pregnant woman’s blood, draw blood and determine whether the fetus is at risk of Down’s syndrome by means of genetic sequencing; 2. 13-16 weeks: Down’s screening can be performed to check the nuchal translucency layer, nasal bone dysplasia, cardiovascular malformation, methemoglobin, free estriol, etc., to determine whether the fetus is abnormal, chromosomal abnormal fetus, after delivery, often accompanied by special facial features, such as dullness, lateral upward slanting of the eyes, intelligent backwardness, growth retardation, developmental malformation, susceptibility to diseases, etc.; 3. 16-20 weeks of gestation: advanced age over 34 years old Pregnant women with Down’s syndrome, those with Down’s syndrome at home, those who have already given birth to a child with Down’s syndrome, and those who are at high risk for blood tests, need to undergo amniocentesis to further check for chromosomal abnormalities and undergo chromosomal implantation for about 7 days to determine whether the baby has abnormalities, such as Down’s syndrome, beta marine anemia, hemophilia, spina bifida, congenital nephropathy, esophageal or intestinal atresia, complete absence of the brain, etc.; 4. 20-28 weeks of gestation -28 weeks: Through 4D ultrasound, the fetus can be dynamically observed in utero, including the development of fetal body surface and internal organs, and cleft lip and palate, abnormal development of central nervous system, internal organ malformation, congenital heart disease, etc. can be checked. Therefore, 16-28 weeks of pregnancy is a critical period for women to have fetal teratology examination. Pregnant women are advised to do regular prenatal checkups to ensure the normal development of the fetus.