The main causes of bleeding before pregnancy include the following: i. If this symptom occurs within 30 days after the last menstrual period, the bleeding is not large, the bleeding time is relatively short, and the blood HCG laboratory test results are significantly elevated, then it is considered to be bleeding at conception. The bleeding is a special manifestation of the process of conception, mainly due to the transient decrease of estrogen level in the body during the process of conception. Second, if the pregnancy is diagnosed late, about 7-10 days after the delay of menstruation, and abnormal bleeding is found before the pregnancy is diagnosed after examination, this bleeding phenomenon is a manifestation of miscarriage. If a gestational sac is formed in the uterine cavity, it is a sign of preterm miscarriage and can be treated with fertility preservation. If there is no gestational sac formation in the uterus, it is a manifestation of biochemical miscarriage and no special treatment is needed.