Bleeding between your periods, heavy periods or periods that last longer than the typical seven days each cycle can be considered abnormal uterine bleeding. It can be tempting to ignore abnormal uterine bleeding, but it should always be reported to your doctor, as it can be caused by some serious underlying conditions. Common Causes Of Abnormal Uterine Bleeding   Abnormal uterine bleeding can be caused by hormonal imbalances, which can occur due to being overweight or failing to ovulate.