There are several causes of PPH, particularly uterine atony, trauma, and retained placental fragments. Several predisposing factors related to these causes can be found in Box 2. The number one cause of early PPH is uterine atony, a condition in which the uterus does not adequately contract, allowing increased blood loss from the placental site of implantation. After the placenta is delivered, the uterus needs to contract to seal off the iliac arteries. If the uterus is contracted, the placental site is smaller, causing less bleeding.

• BOX 2 Predisposing Factors to Postpartum Hemorrhage

Overdistension of the uterus (multiple gesta- Forceps or vacuum delivery tion, hydamnios) Prolonged or rapid labor

Grand multiparity Extended used of oxytocin (Pitocin) during Use of anesthetic agents, especially halothane labor

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• BOX 2 Predisposing Factors to Postpartum Hemorrhage (continued)

Delivery of large infant Manual removal of the placenta Placenta previa

Placenta accreta (separation of the placenta is difficult or impossible) Mismanaged/prolonged (>30 minutes) third stage of labor

Maternal malnutrition or anemia Uterine infections Pregnancy-induced hypertension Maternal history of hemorrhage or blood coagulation problems

Lacerations of the perineum, vagina, and cervix can occur during a vaginal birth. Lacerations of the cervix occur with rapid dilation or with pushing before complete dilation. During the second stage of labor, vaginal, perineal, and periurethral tears occur. Failure to repair these lacerations adequately can result in a slow, steady trickle of blood.

The most common cause of late PPH is retained placental fragments. If parts of the placenta remain in the uterus after delivery, small clots form around the retained parts, sealing off the bleeding. After a while the clots slough, and heavy bleeding occurs. Subinvolution (delayed involution) can also be a causative factor in a late PPH.

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