Normally, women shed their uterine lining every month, causing capillary rupture and bleeding, and the blood, mixed with the shedding of the uterine lining, is discharged from the vagina. However, in some women, due to certain factors, the menstrual blood cannot be discharged from the vagina, but flows back to the uterus through the fallopian tubes to the abdominal cavity and other parts of the body, which belongs to the reverse menstrual blood flow. If the amount of refluxed menstrual blood is relatively small, it usually has no adverse effect and will be gradually absorbed by the lining of the abdominal cavity. If menstrual blood reflux occurs regularly and the amount of refluxed blood is relatively large, the menstrual blood cannot be completely absorbed in the abdominal cavity, and it is easy to form a mass in the pelvis. Reflux of menstrual blood is also likely to bring endometrial fragments to the abdominal cavity and ovaries and other parts of the body, resulting in endometriosis, causing more serious symptoms such as menstrual cramps, and in some cases, endometriosis may occur to the myometrium, resulting in adenomyosis, which will affect the health of the female body.