Exaggerated placental site, consisting of implantation site intermediate trophoblasts, causes massive postpartum uterine hemorrhage: case report and literature review.

Every year, 14 million cases of obstetric hemorrhage occur worldwide, causing 127,000 maternal deaths. About 75% of postpartum hemorrhage cases are due to atonic uterus, which is loss of uterine muscular tone or strength for contraction of the uterus after delivery. The prediction of atonic uterus is therefore important for the prevention of postpartum maternal death. However, prediction of occurrence of atonic uterus is difficult before delivery, because the precise pathophysiological mechanism to trigger this condition remains unclear. Here, we present a case of severe postpartum hemorrhage due to atonic uterus. A 35-year-old woman gave a birth by vaginal delivery to a healthy boy. However, due to intractable massive hemorrhage after the removal of the retained placenta, we performed supravaginal hysterectomy as the best option for survival. Pathological examination showed that implantation site intermediate trophoblasts (ISITs) formed unusually large clumps in the decidua, diagnosed as exaggerated placental site (EPS). EPS is thought to be a condition consisting of an excessive number of ISITs. ISITs are differentiated from a trophoblast lineage in the process of placenta formation. ISITs anchor the placenta to the maternal tissue and are considered to maintain pregnancy, but the postpartum role of these cells remains unclear. Excessive infiltration of ISITs, namely EPS, may cause postpartum atonic uterus. In this article, we also reviewed the literatures on EPS. The present case and other reported cases indicate that EPS causes mass formation in the uterus, continuous uterine bleeding, and massive hemorrhage, resulting in hysterectomy.