Women may have two periods a month due to: 1. endocrine dysfunction, such as estrogen, sex hormone, progesterone and luteinizing hormone deficiency, resulting in the loss of normal regulation of menstruation, resulting in the situation of two periods a month. 2. ovulatory bleeding caused by relatively small amount of bleeding 2-3 days can subside on its own, the longest does not exceed 7 days. This condition is mostly caused by the decrease of estrogen and progesterone in the body during ovulation and the retreating bleeding of the endometrium.3. It may also be caused by rare diseases, such as endometrioma, uterine plasmacytoma, endometrial rhabdomyosarcoma and vaginal rhabdomyosarcoma, etc. These abnormally proliferating tumors can cause certain interference with the formation of menstruation. The harmful substances produced by the tumors can disrupt the hormone levels in the body, which can lead to menstrual disorders and the occurrence of twice-a-month periods.