Although a girl's or woman's menstrual flow can vary from light to heavy, the average amount of blood lost during a period is nearly 3 tablespoons, notes the University of North Carolina's Department of Obstetrics & Gynecology. However, many women can experience frequent heavy bleeding during their menstrual cycle, and this can lead to anemia. In some cases, abnormally heavy bleeding may be a symptom of an underlying condition.
Heavy bleeding is defined as losing 5 tablespoons of blood during a period. Some women can lose up to 2 cups, which is a pint of blood. Losing this much blood can cause anemia. Menorrhagia is the term used for a heavy period that can last more than 7 days and in which blood loss is heavy, notes WebMD.
There are many underlying conditions that can cause abnormally heavy bleeding, including fibroids, pelvic inflammatory disease and cancer. For these reasons, it is important that women with heavy menstrual bleeding issues see a doctor for a diagnosis.