In addition to confirming whether the pregnancy is intrauterine during early pregnancy, whether the embryo is viable or not, and confirming the fetal orientation and size of the fetus before delivery, the following three times are more important. 11-13+6 weeks of pregnancy : 1. The main purpose is to screen the fetus for chromosomal markers (NT thickness, nasal bone if necessary, venous catheterization blood flow spectral pattern, etc.); 2. To make a diagnosis of certain severe fetal structural malformations (anencephaly, severe brain enlargement, severe open spina bifida, severe thoracic and abdominal bifida with externalization of the internal organs, etc.). 20~24 weeks of pregnancy: 1. The main purpose is to screen and diagnose fetal structural malformations; 2. To screen for certain chromosomal abnormalities (nasal bone, ventricular punctate echogenicity, mild dilatation of the renal pelvis, choroidal cyst, mild dilatation of the cerebral ventricles, mild shortening of the femur, and strong echogenicity of the intestines, etc.); and to provide valuable information for the choice of termination of pregnancy prior to perinatal period for fetuses with serious structural malformations and serious hereditary disorders. Information. Late pregnancy (32-34 weeks of gestation): 1. The main purpose is to assess fetal survival (presence of fetal distress, etc.); 2. To pick up fetal structural malformations (e.g., gastrointestinal obstruction, renal lesions, etc.). Provide valuable information for the fetus that should be born as close as possible to the expected date of birth or choose the right time for birth. (Special note: Prenatal ultrasound examination is voluntary for pregnant women)