Miscarriage refers to the spontaneous expulsion of the gestational sac from the uterine cavity, without the need for human intervention. Human interventions mainly include medical abortion or painless surgical abortion. During a miscarriage, the gestational sac is expelled from the uterus, so the expelled material is primarily the gestational sac. The sac generally consists of white villous tissue, and during a natural miscarriage, it is essential to identify villous tissue in the pregnancy tissue in order to confirm a natural miscarriage. Besides the villous tissue, due to decidualization changes in the endometrium after pregnancy, the tissue expelled during a miscarriage also contains a certain amount of decidual tissue. Therefore, the material expelled in a natural miscarriage mainly includes the villous tissue, followed by uterine decidual tissue.