Every girl has such an unpredictable relative that you can only suffer in silence. The most distressing thing is that it is difficult to feel the temper of this relative, but there is a pattern to the menstrual cycle, which is the first day of the incoming period to the first day of the next period. The average menstrual cycle for adult women is 21-35 days, with an average of 28 days. The length of the menstrual cycle varies with each woman as follicles mature and are discharged at different times. It is within the normal range to appear 7-10 days early or wrong, and as long as a certain regularity can be maintained it is not considered as menstrual irregularity, meanwhile, the normal period for women is 3-7 days, with an average of about 4-5 days, so there is no need to worry even if the period is less than 7 days. The menstrual cycle, also called the ovarian cycle, is divided into four phases, including the follicular phase, ovulation, luteal phase and menstrual phase: 1. Follicular phase The follicular phase is from the first day of menstruation to the day of ovulation. During this period, the follicle stimulating hormone increases the concentration of estrogen hormone in the body, the follicle matures and the endometrium thickens. 2. Ovulation Ovulation is the process in which the egg cells are expelled together with the surrounding granulosa cells of the oocyte mound. The date of ovulation in women is usually about 14 days before the next menstrual period. 3. Luteal phase The luteal phase refers to the day after ovulation to the day before menstruation. The ovaries are influenced by luteinizing hormone, which secretes luteinizing hormone to maintain the thickened endometrium for the fertilized egg to lay. 4. Menstrual period The duration of each menstrual period is called menstrual period, which is usually 2-8 days, with an average of 4-6 days. Usually there are no special symptoms during menstruation, but during menstruation, due to pelvic congestion and the action of prostaglandins, some women may experience discomfort in the lower abdomen and lumbosacral region or painful contractions of the uterus, and may have symptoms of gastrointestinal disorders such as diarrhea. Menstruation is the result of cyclical changes in the endometrium under the action of ovarian hormones. Stress, emotional instability, late nights, and irregular diet can affect ovarian hormones, so the cycle is not as accurate as one might think. Women should develop a habit of recording their menstrual cycle so that they can know approximately when they are menstruating, and if there are irregularities, they should come to the hospital for a timely examination. References: [1] Zheng Youhong,Wang Yifeng. Endometrial changes and mechanisms in the normal human menstrual cycle [A]. Shandong medicine 2016,56(7):90