The menstrual cycle can be divided into follicular phase (proliferative phase), luteal phase (secretory phase) and menstrual phase according to the changes in the ovaries and the endometrium. ①The period from the cessation of menstruation to the end of ovulation is called the follicular phase. At the beginning of this period, both estrogen and progesterone in the blood are at low levels, until about a week before ovulation, the concentration of estrogen in the blood rises rapidly, and reaches its peak a day or so before ovulation. During the follicular phase, the endometrium thickens, the glands increase and become longer, so it is also called the hyperplasia phase. From ovulation until the next menstrual period, it is called the luteal phase. During this period, the concentration of progesterone in the blood increases significantly. The endometrium is stimulated by progesterone on top of estrogen, and the glycogen content of endometrial cells increases, and the glandular ducts secrete mucus containing glycogen, so it is the secretory phase. If the egg is not fertilized, the corpus luteum degenerates and enters the menstrual phase; if conception occurs, the corpus luteum develops into the corpus luteum of pregnancy, which can continue to secrete progesterone and estrogen, and the endometrium continues to thicken by the action of estrogen and progesterone to form the meconium. ③ From the onset of menstruation to the cessation of bleeding, it is called the menstrual period. During this period, the content of estrogen and progesterone in the blood rapidly decreases to the most generative level, spasmodic contraction of endometrial blood vessels occurs, followed by endometrial shedding and bleeding, which is the menstrual period.