Definition of menstruation: A sexually mature woman undergoes cyclic changes in the endometrium due to the action of sex hormones secreted by the ovaries, and sheds the mucous membrane and blood once a month through the vagina, a bleeding phenomenon that is known as menstruation. The formation of menstruation: Menstruation is regulated by the interaction between the reproductive hormones of the hypothalamus, pituitary and ovaries. During the menstrual and proliferative phases of the menstrual cycle, the levels of estradiol and progesterone in the blood are low, thus weakening or eliminating the negative feedback effect on the pituitary and hypothalamus, leading to an increase in the secretion of gonadotropin-releasing hormone by the hypothalamus, which in turn leads to the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary. This leads to an increase in follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion by the pituitary gland, thus causing follicle development. As the follicle matures, estrogen peaks, which has a positive feedback effect on the hypothalamus, prompting the pituitary gland to release large amounts of LH, which peaks and acts synergistically with FSH to cause ovulation of the mature follicle. After ovulation, both circulating LH and FSH drop sharply and the corpus luteum is formed and gradually develops and matures. The corpus luteum mainly secretes progesterone, which transforms the endometrium into a secretory phase. The corpus luteum also secretes estrogen at the same time. Due to the joint negative feedback effect of large amount of progesterone and estrogen, the LH and FSH secretion by pituitary gland decreases accordingly, the corpus luteum starts to shrink, and the secretion of progesterone and estrogen also decreases. The endometrium loses the support of sex hormones and undergoes necrosis and shedding, resulting in menstruation. At this point, estrogen and progesterone decrease and the next menstrual cycle begins again. It can be seen that the production of menstruation is mainly dependent on fluctuations in hormone levels, and ovulation is only one of the reasons for changes in hormone levels. Some women have periodic bleeding but are unable to ovulate, which is medically known as anovulatory abnormal uterine bleeding, and this is often mistaken for menstruation. Patients with adolescent gonorrhea have blood estrogen levels within the normal range for women of childbearing age, but no blood LH and FSH peaks in the middle of the normal menstrual cycle, due to an abnormal hypothalamic-pituitary positive feedback response to estrogen. It takes time for the normal function of the CNS-hypothalamic-pituitary-ovarian axis to be established during puberty. If stimuli such as overexertion, stress, or genetic factors such as obesity or insulin resistance are present at this time, it may cause anovulatory bleeding. In perimenopausal women, at this time, women with low follicular reserve, reduced sensitivity to gonadotropins, or reduced responsiveness of the hypothalamus-pituitary to positive feedback regulation of sex hormones, may first experience luteal insufficiency, intermittent or irregular ovulation, and eventually ovulation stops. At this time, the follicles still develop to some extent, but slowly and inadequately, or degenerate irregularly, not enough to cause positive feedback, resulting in insufficient or absent progesterone levels and the onset of bleeding. In conclusion, there is no causal relationship between ovulation and menstruation, and clinically it is difficult to determine whether the nature of the bleeding is menstrual or not by symptoms alone. Therefore, it is inappropriate to determine whether ovulation has occurred by the presence or absence of menstruation. It is recommended that women consult a regular hospital for other more scientific and reliable ways to monitor ovulation.