If a spontaneous abortion occurs in the second trimester of pregnancy, the following reasons are common in clinical practice:1. The most common reason is caused by embryonic gene deletion, which makes it difficult to achieve full-term delivery, and the embryo often stops developing in the early stages of pregnancy, resulting in spontaneous abortion.2. The spontaneous abortion can be caused by the pregnant woman suffering from a certain kind of disease, such as serious internal medicine disease, liver and kidney function abnormality, or coagulation dysfunction, all of which can lead to the occurrence of spontaneous abortion.3. The phenomenon of spontaneous abortion occurs. 3, because of sexual exertion after the first sign of abortion, not timely treatment, and ultimately lead to spontaneous abortion. 4, uterine developmental deformity can also lead to spontaneous abortion. Therefore, it is recommended to do the necessary health checkups after recovering from spontaneous abortion to understand the basic condition of the body and whether the endocrine abnormality is present.