The normal menstrual cycle is within 21 to 35 days, and any menstrual cycle within this range is normal. The formation of the menstrual cycle has a lot to do with the secretion function of the ovaries. The lining of the uterus is affected by the hormone levels of the ovaries, and the cycle of shedding occurs, which leads to menstruation. Therefore, whether a woman’s menstrual cycle is regular or not has a lot to do with ovarian function. Most women have a regular menstrual cycle, usually with a difference of about 2-3 days. However, patients with unstable ovarian function, polycystic ovary syndrome, irregular menstruation and abnormal ovulation are significantly more likely to occur. And women with irregular menstrual cycles have an increased difficulty in getting pregnant. So if menstruation is not normal, it is still necessary to make adjustments.