Menstruation is vaginal bleeding caused by the peeling of the endometrium and is usually dark red in color, with a small percentage combined with blood clots. Most menstrual blood is liquid and does not clot. The normal menstrual cycle is 28-30 days, the menstrual period is 3-7 days, and the volume is 30-80 ml. Between the ages of 45 and 55, normal women will gradually enter the perimenopausal phase due to the decline of hormones and the gradual decline of ovarian function, which means that menopause is approaching. The menstrual cycle can be shortened or lengthened, and the menstrual volume can increase or decrease gradually, and may be combined with psychoneurological symptoms such as hot flashes, night sweats, dizziness, fatigue, mood swings, lack of concentration, and insomnia. In the perimenopausal period, the menstrual blood should still be dark red when the volume is high and brown when the volume is low, after which the menstruation will gradually decrease until it stops as estrogen decreases. Menstruation is considered menopausal if it stops for more than a year and comes back. In short, when menopause is approaching, there will be significant changes in menstruation, whether in color, volume or cycle, in response to hormonal changes. Any abnormalities in menstrual cycle, period, volume or color of menstrual blood should be seen by a doctor for timely and proper treatment.