The menstrual cycle is the interval between the first day of menstruation and the first day of the next menstruation. The normal menstrual cycle is 21-35 days, and the average menstrual cycle is 28 days. The whole menstrual cycle consists of the menstrual period, the proliferative period and the secretory period. If we take 28 days as a menstrual cycle, the menstrual phase is the 1st-4th days of the menstrual cycle, during which progesterone and estrogen decrease and the endometrium is shed to form menstrual blood; the proliferative phase is the 5th-14th days of the menstrual cycle, during which the follicles develop and mature; the secretory phase is the 15th-28th days of the menstrual cycle, which is equivalent to the luteal phase, during which the endometrium thickens and is in a secretory state, which is conducive to The endometrium thickens and is in a secretory state, which is conducive to the fertilization of the egg. The menstrual cycle is influenced by the hypothalamus, pituitary gland and ovaries, most women have a menstrual cycle of 28-30 days, occasionally women have a longer menstrual cycle, which can reach 3 months or even 1 year.