Overview of Postpartum Hemorrhage VIDEO Causes The most common cause of postpartum hemorrhage is Uterine atony Risk factors for uterine atony include Uterine overdistention (caused by multifetal pregnancy, polyhydramnios, fetal anomaly, or an abnormally large fetus) Prolonged labor or dysfunctional labor Grand multiparity (delivery of ≥ 5 viable fetuses) Relaxant anesthetics Rapid labor Intra-amniotic infection (chorioamnionitis) Other causes of postpartum hemorrhage include Lacerations of the genital tract Extension of an episiotomy Uterine rupture Bleeding disorders Retained placental tissues Hematoma Uterine inversion Intra-amniotic infection Subinvolution (incomplete involution) of the placental site (which usually occurs early but may occur as late as 1 month after delivery) Uterine fibroids may contribute to postpartum hemorrhage.