The common term for the major teratology examination is “mid-pregnancy systematic prenatal ultrasound examination”. The time of examination: 22-26 weeks of pregnancy, when all major organs of the fetus have developed, the amniotic fluid volume is moderate and the imaging effect is good, which is more conducive to the systematic screening of fetal malformations. The main screenings are: anencephaly, severe brain expansion, severe open spina bifida, severe abdominal wall defect and visceral ectasia, single-chambered heart, lethal chondrodysplasia, limb malformation, etc. What is “small teratology”? The fetus has been in the process of growth and development, and some structural malformations are in dynamic development, which can only be observed by ultrasound at certain gestational weeks, such as microcephaly, hydrocephalus, diaphragmatic hernia and certain heart malformations, and the teratology examination at this time is generally called small teratology examination. Examination time: 30-32 weeks of pregnancy. The main screening tests: hydrocephalus, hydronephrosis, polycystic kidney, duodenal atresia, pneumocystic adenoma, etc. To pick up the mid-trimester major abnormalities, as well as to detect late-onset malformations. Can major and minor teratology be substituted for each other? No, minor teratology examination shows the fetal baby’s heart, lungs and kidney structures clearly, but it shows the limbs and spine less well than in middle pregnancy, and it is not as good as major teratology for taking facial 4-dimensional imaging. Major and minor teratology have their own significance, importance and complementarity of examination.