A normal menstrual cycle is 28 days, but anything plus or minus seven days is considered normal, making it possible to have two periods in one month as little as 21 days apart, according to eMedicineHealth. However, if periods are consistently closer than that, the abnormal bleeding is called metrorrhagia and can be a cause for concern. Possible reasons for an extra period include hormonal changes or dysfunctional uterine bleeding.
Dysfunctional uterine bleeding is the most common cause of bleeding at abnormal times between periods in women of childbearing age, according to eMedicineHealth. In most cases, it does not indicate disease, and can occur both with and without the release of an egg from the ovaries.
In some cases, abnormal bleeding outside of the normal menstrual cycle can indicate uterine fibroids or pelvic inflammatory disease, according to eMedicineHealth. If two periods monthly continue to occur, visit a doctor for an evaluation and pelvic examination to rule out these conditions. In older women, irregular periods can be an early indication of the beginning of menopause. Any time that irregular bleeding is accompanied by severe abdominal pain, lightheadedness or a fever, it is important to seek medical attention as soon as possible.