The endometrium is shed during menstruation, so many patients have menstrual bleeding with flesh-like tissue or membrane-like tissue, mainly because the patient’s menstrual blood is mixed with endometrium and mucus, not just blood. Menstruation is caused by the cyclical proliferation and exfoliation of the endometrium of the uterus. Before menstruation and after luteal atrophy, the patient’s estrogen and progesterone levels drop rapidly, causing the endometrium to lose its high hormonal support, and therefore to exfoliate and bleed. After the onset of menstruation, the estrogen and progesterone levels rise again, causing the endometrium to proliferate and secrete under the action of hormone levels, and then the hormone levels drop, resulting in exfoliation and bleeding.