Uterine atony

The failure of the myometrium to contract adequately after delivery, resulting in a soft, enlarged, hypotonic uterus that cannot compress uterine blood vessels and is the leading cause of early postpartum hemorrhage. Possible causes are uterine overdistension (twins), prolonged labor, extremely fast labor, medications (oxytocin, MgSu), uterine fibroids, and chorioamnionitis.