Two periods a month, 15 days apart, mostly unrelated to coitus, may be related to endometrial polyps, uterine fibroids, luteal insufficiency, etc., but sometimes it is also a normal menstrual cycle. 1. Endometrial polyps: after suffering from endometrial polyps, there may also be a small amount of bleeding, which is mistaken for menstruation. 2. Uterine fibroids: For those who suffer from uterine fibroids, when the fibroids are large and affect the lining of the uterus, it may also lead to short intervals between menstruation. 3. Luteal insufficiency: When the luteal function is not fully secreted, it may also lead to abnormal shedding of the uterine lining, causing vaginal bleeding. 4. Normal menstrual cycle: The menstrual cycle is calculated from the first day of menstruation, and the normal menstrual cycle is 21~35 days. If a woman has her period for 7 days, it is normal for her period to come back again in 15 days’ interval. If you regularly have two periods a month, and the interval of 15 days, it is recommended to go to the hospital in a timely manner, after the doctor’s interview, combined with the patient’s own condition and the results of the relevant programs, to determine the cause of the disease after targeted treatment.