The time of prenatal checkups is as follows: 1. The first major checkup: NT examination at 12 weeks of gestation, i.e. nuchal translucency layer thickness examination, if there is no abnormality in the NT examination result, generally speaking, relatively systematic related laboratory tests are required, which include about seven tests; 2. The second major checkup: systematic ultrasound examination at 20 to 24 weeks of gestation to further rule out fetal structural abnormalities; 3. The third major checkup: ultrasound and fetal monitoring examination at 36 weeks of gestation.