Heavy bleeding late in pregnancy usually indicates a complication with the placenta. This requires medical treatment. The two most common complications are: Placenta previa. This is when the placenta has developed at the bottom of the uterus, covering the cervix. This usually does not cause any pain, but can cause vaginal bleeding. Placental abruption. In most pregnancies, the placenta is connected to the uterine wall. If it becomes disconnected, either before or during labor, it can disrupt circulation to the baby. Vaginal bleeding is sometimes present, but more often it will cause abdominal pain