The hypothalamus-pituitary-gland-ovary constitutes an axis system (HPOA), in which the hypothalamus regulates pituitary function, the pituitary gland regulates ovarian function, and ovarian hormones then act on various target organs such as the uterus, etc. Meanwhile, ovarian hormones have positive and negative feedback regulation on the hypothalamus-pituitary gland, and the normal function of HPOA is one of the basic conditions for maintaining female fertility. The normal physiology of menstruation, egg development and maturation, fertilization, and early embryo implantation and development are all regulated by the endocrine and nervous systems and depend on a normal endocrine environment in the body. The normal female ovary undergoes 1 cycle per month. During the early follicular phase, serum follicle-stimulating hormone (FSH) levels gradually increase and a group of sinus follicles are recruited in the ovary. FSH causes granulosa cells to continue to proliferate, activates cytochrome P450 aromatase in granulosa cells, and promotes the synthesis and release of estradiol (E2). By day 7 of the menstrual cycle, the developing follicular cluster is recruited and the follicle with the lowest FSH threshold develops preferentially into the dominant follicle, which produces and secretes more E2, which feedback inhibits pituitary FSH secretion and gradually degrades the other follicles. The dominant follicle determines the duration of the follicular phase of the cycle, and the serum and follicular fluid E2 levels are positively correlated with the volume of the dominant follicle. On day 11-13 of the menstrual cycle, the dominant follicle enlarges rapidly and secretes E2, reaching about 300 pg/ml (1100 pmol/L). Due to the positive feedback effect of the E2 peak, the pituitary gland releases luteinizing hormone (LH) and FSH in large amounts, allowing the oocyte to eventually mature and ovulation to occur. The luteal corpuscles produce and secrete progesterone (P) and E2 in preparation for the admission of the pregnant egg and maintenance of early embryonic development. The luteal corpuscles function most vigorously 5-10 days after ovulation.