There are many reasons for early menstruation, which may be a normal phenomenon, or it may be caused by ovulation disorders, luteal insufficiency, premature ovarian failure and so on. 1. Normal phenomenon: the normal menstrual cycle of women is between 21 days and 35 days, if the menstrual period is one week ahead of schedule, it is within the normal range and does not need special treatment. 2. Ovulation disorders: Because ovulation disorders can cause the corpus luteum to atrophy faster, the endometrium’s proliferative and secretory phases are shortened, and the menstrual cycle is shortened, which may cause menstruation a few days earlier. 3. Luteal insufficiency: if you suffer from luteal insufficiency, due to endocrine disorders caused by luteal insufficiency, it will make the corpus luteum atrophy prematurely, which may cause menstruation a few days earlier. 4. Premature Ovarian Failure: If a woman suffers from premature ovarian failure, due to the premature decline in ovarian function, the follicle develops prematurely in the decline of ovarian reserve function, which may cause menstruation a few days earlier. When this happens, attention should be paid and medical treatment should be sought as soon as possible.