The four common causes of postpartum hemorrhage are often referred to as “the four T’s.”  ► Tone. Uterine muscles do not contract properly and cause blood vessels to continuously bleed.  ► Trauma. Damage to the uterus, vagina, cervix, or perineum can cause excessive bleeding.  ► Tissue. Sometimes the placenta does not completely detach from the uterine wall. ► Thrombin. Other conditions that may cause blood clotting can exacerbate postpartum hemorrhage.