WebMD states that a wide number of conditions can cause a woman to experience heavy periods. Hormonal imbalances, common in young women who have just recently begun menstruating and in women with ovarian malfunctions, can cause heavy periods. Fibroid tumors, which most often occur in the uterus, cause heavy periods.
WebMD also notes that a miscarriage or ectopic pregnancy can cause a heavy period, as can the use of blood thinners or a nonhormonal intrauterine device. Pelvic inflammatory disease and feminine cancers can also cause heavy bleeding. Any condition that impacts the clotting of blood can cause heavy menstruation. Heavy periods can usually be treated.