Symptoms of retained placenta include prolonged vaginal bleeding, abdominal pain, and even infection. 1. prolonged vaginal bleeding: when the post-partum ultrasound examination suggests that some placental tissue remains in the uterine cavity, it will affect the uterus to restore the uterus and make the blood sinus of the placental peeling surface close incompletely, which will lead to prolonged vaginal bleeding and increase in the amount of symptoms. 2. Abdominal pain: it is caused by the contraction of the uterus due to the stimulation of the uterus by the placenta tissue left in the uterine cavity. 3. Infection: when the placental tissue remains in the uterine cavity for a long time, it may cause infection, which is manifested by the increase of bloody discharge, lasting for a long time, accompanied by foul smell and other manifestations, and also high fever and other symptoms. When the ultrasound examination suggests that the placenta remains in the uterine cavity, you need to be actively treated under the guidance of the doctor.