There are more reasons for a 40-year-old woman to have her period twice a month, which may be caused by ovulation bleeding, contact bleeding, dysfunctional uterine bleeding and so on. 1. Ovulation bleeding: During ovulation, the level of estrogen in the body may decrease, which may lead to bleeding during ovulation, but the amount of bleeding is usually less and lasts for a shorter period of time. 2. Contact bleeding: If there are abnormal lesions in the cervix or endometrium, there may be a small amount of vaginal bleeding after coitus or other examinations. 3. Dysfunctional uterine bleeding: because after 40 years old, women’s hormone level may have abnormal secretion, which will lead to irregular shedding of the uterine lining, which will lead to irregular menstruation, twice a month. There may be other reasons for 40-year-old women to have 2 periods per month, so it is recommended to consult a doctor in time to improve the relevant examinations, to clarify the cause of the disease under the guidance of a professional doctor, and to choose the appropriate treatment plan.