A woman’s monthly menstruation is an outward sign of reproductive maturity. Before puberty, the ovaries are basically non-functional. After puberty, under the action of pituitary gonadotropins, follicles begin to develop gradually and estrogen is synthesized at the same time, and when the follicles mature and ovulate, they become corpus luteum. The corpus luteum synthesizes estrogen and at the same time produces progesterone. As the ovaries change, the endometrium is affected by the ovaries and undergoes corresponding cyclic changes. Estrogen causes the endometrium to thicken and the endometrial cells to enlarge and increase, leaving the endometrium in a proliferative state. After ovulation, due to the combined effect of estrogen and progesterone, the endometrium becomes edematous, the blood vessels under the endometrium become tortuous, and finally rupture and bleed, which clinically manifests as menstruation.