The endometrium changes with the menstrual cycle, and usually women with endometrial thickness of 10-12mm will experience endometrial exfoliation and menstruation. The endometrium is very thin, about 0.5-0.6cm, when menstruation just clears; it gradually thickens during the proliferative phase and can reach 0.9cm during ovulation; it further thickens when it enters the secretory phase and can reach 10-12mm before menstruation; the endometrium will shed on its own after luteal atrophy and form the menstrual flow. However, the thickness of the endometrium before menstruation may vary due to factors such as different body types and different endocrine conditions. In addition, if the endometrium is thin, the amount of blood after menstruation will be less, while the amount of menstrual blood will be greater in those with thicker endometrium. If the endometrium is too thick or too thin before menstruation, sex hormone six and other related tests should be done, etc., and symptomatic treatment should be carried out under the guidance of the doctor according to the test results.