Menstruation coming 12 days earlier may be caused by biological factors, medication factors, or by organic uterine diseases, hormone level disorders, pregnancy-related diseases and other reasons. 1. Biological factors: Generally speaking, menstruation is not only affected by hormone levels, but also by the living environment, emotional stress, diet and nutritional factors, so it may lead to early menstruation. 2. Drugs: If you take drugs containing hormones, such as birth control pills, progesterone and dydrogesterone tablets, it may lead to early menstruation. 3. Organic lesions of the uterus: If the patient suffers from endometrial polyps or uterine fibroids and other organic lesions, it will lead to an increase in the area of the uterine lining, causing early menstruation. 4. Hormone level disorders: If the female hormone level decreases, and the patient has decreased ovarian function or luteal insufficiency, then it may also lead to early menstruation. 5. Pregnancy-related diseases: If a woman has had unprotected sex, then the bleeding may not be menstruation, but may be caused by abnormal vaginal bleeding due to pre-miscarriage or ectopic pregnancy. There are many reasons for early menstruation in the clinic, so we recommend that you consult a doctor in time to identify the cause of the problem and then target treatment.