A 40-year-old woman who suddenly has two periods a month may be a normal physiological phenomenon, but may also be caused by endocrine disorders, gynecological diseases, medication factors. It is recommended to consult a doctor in time to find out the cause, under the guidance of the doctor treatment. 1. Normal physiological phenomenon: women’s normal menstrual cycle is usually between 21 to 35 days, if the beginning of the month, at the end of the month, there may also be a normal menstrual flow, is a normal phenomenon, do not need to worry too much. 2. Endocrine disorders: may be related to factors such as insufficient secretion of progesterone, which can affect a woman’s menstrual cycle, so that the menstrual cycle is too short or too long, can lead to a month of two menstruation. 3. Gynecological diseases: for example, uterine fibroids, cervical polyps, endometrial polyps, etc., the aggravation of the lesions may lead to non-menstrual vaginal bleeding, which is misdiagnosed as menstruation, and may be accompanied by odor of secretion, increase in secretion, and pain in the abdomen and other symptoms. 4. drug factors: women in the reproductive age, in the ovulation period did not take effective contraception, oral emergency contraceptive pills, easy to cause withdrawal bleeding, it is mistaken for menstruation. A 40-year-old woman who suddenly has her period twice a month and is accompanied by other obvious abnormalities should be alerted to disease factors, and it is recommended to seek medical examination and treatment.