Vaginal bleeding will occur if the fertilized egg does not settle and the chorionic gonadotropin value will gradually decrease, and the early pregnancy reactions such as nausea, vomiting, drowsiness and frequent urination will gradually disappear. Vaginal bleeding will occur about 3-7 days after the delayed menstruation, and the bleeding volume will be similar to the usual menstrual volume, and there will be a menstrual flow. When these symptoms occur, it indicates the occurrence of biochemical pregnancy, which refers to the failure of the fertilized egg to settle, withering and death. There are many reasons why a fertilized egg does not implant. It may be due to the poor quality of the fertilized egg which dies before it reaches the uterine cavity, or there are certain diseases in the body, such as tubal inflammation, tubal development problems, tubal tumors, uterine development malformations, endometritis, etc., which may cause the fertilized egg not to implant properly.