The endometrium will change with the ovarian hormone cyclic changes, the thinnest just after menstruation, thicker before menstruation, double thickness, since the menstrual period lineal thickening to 10mm, usually not more than 12mm. The endometrium is divided into the functional layer and the basal layer. The functional layer is affected by the ovarian hormonal changes and has cyclic proliferation, secretion and exfoliation changes. On the 5th to 14th day of the menstrual cycle, the thickness of the double layer of endometrium is 0.5mm, proliferating to 3-5mm. On the 24th to 28th day of the menstrual cycle, which is the pre-menstrual period, the endometrium is spongy, and the double layer is up to 10 millimeters thick, usually not more than 12 mm. After the withdrawal of progesterone and estrogen from the body, the functional layer of the endometrium disintegrates and falls off from the bottom layer, and fragments of the dislodged endometrium and blood flow out of the vagina together, i.e., the onset of menstruation.