Refers to pregnancy loss before 28 weeks of gestation. Miscarriage before the third trimester refers to early miscarriage and late miscarriage from the third trimester to 28 weeks of pregnancy. The chance of occurrence is 1/6. Etiology 1. Random chromosomal/genetic abnormalities: A normal pregnancy requires a normal egg and a normal sperm, which combine to form a ligand that develops after implantation in the uterus. This is a complex process and it is inevitable that some problems will occur during this period. 60-70% of early pregnancy miscarriages are abnormal (natural or assisted reproduction) and this occurs randomly and the mechanism of occurrence is not clear. There are no drugs available to prevent or treat miscarriages caused by chromosomally abnormal embryos. 2. Parental chromosomal abnormalities A very small percentage of parents with abnormal chromosomes will cause fetal abnormalities. It can be diagnosed by peripheral blood chromosome test. 3.Uterus abnormalities Normal uterine morphology is very important for embryo implantation. Abnormal uterine morphology such as longitudinal uterus can increase miscarriage. Uterine fibroids can also cause miscarriage if they compress the uterine cavity enough. These abnormalities will be diagnosed and treated by the doctor. 4, other diseases Endocrine abnormalities such as abnormal thyroid function and uncontrolled diabetes can increase miscarriage, but these diseases can be treated. 5. Immune factors Anti-cardiolipin antibody syndrome, immune antibodies, and abnormal sperm DNA fragmentation may cause miscarriage. Immunotherapy can be performed. Treatment 1.Identify the cause of miscarriage. 2.Treat the cause of miscarriage symptomatically. 3.Genetic examination before embryo implantation.