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Postpartum hemorrhage, or excessive blood loss following delivery, is the leading cause of maternal death worldwide. It is traditionally defined as blood loss greater than 500 mL after vaginal delivery and 1000 mL after a cesarean section.1 This is impractical because the normal blood loss is believed to be 300 to 500 mL following a vaginal delivery and 900 to 1200 mL following a cesarean section.2 It has also been defined as blood loss that results in a decrease in the hematocrit of greater than 10 points between admission and the postpartum period, which corresponds to the 97th percentile of vaginal and 92nd percentile of cesarean deliveries.1,2 A clinically useful definition is excessive bleeding that results in signs and/or symptoms of hypovolemia (e.g., tachycardia, hypotension, oliguria, dizziness, palpitations, syncope, and/or shortness of breath), which corresponds to a 10% or more loss in total blood volume.3 Postpartum hemorrhage can occur at sites within or external to the genitourinary tract (Table 135-1).

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Table 135-1 Anatomic Sites of Postpartum Hemorrhage
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The incidence of postpartum hemorrhage ranges from 4% to 6% of pregnancies in the United States.3 Primary postpartum hemorrhage accounts for greater than 90% of all cases and occurs within 24 hours of delivery. It is most commonly the result of excessive bleeding from the placental implantation site (uterine atony) or trauma to the genital tract. It can be associated with a considerable drop in hematocrit and significant maternal complications. Secondary postpartum hemorrhage occurs more than 24 hours after delivery and up to 12 weeks postpartum. It is usually the result of excessive bleeding from the placental implantation site or retained products of conception, but can also be caused by an infection or coagulation defects.3,6 This chapter reviews the pathophysiology of early postpartum hemorrhage, discusses the diagnosis and assessment of postpartum hemorrhage, and concludes with strategies for treatment.

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The most common causes of postpartum hemorrhage are uterine atony (70% to 90%), genital tract trauma (5% to 8%), retained products of conception (3% to 5%), and hematologic or coagulopathic abnormalities (<2%). Uterine inversion is a rare cause of postpartum hemorrhage. Risk factors for uterine atony include a prolonged third stage of labor, induced or augmented labor, high parity, an overdistended uterus, use of uterine relaxing agents, chorioamnionitis, some types of anesthesia, and previous postpartum hemorrhage.1 Genital tract injuries include vaginal or cervical lacerations, episiotomies, vulvar or vaginal hematomas, and uterine rupture. Retention of all or part of the placenta interferes with uterine contraction, resulting in continued bleeding from the implantation site. Hematologic abnormalities include von Willebrand's disease, disseminated intravascular coagulation, and other less common inherited, congenital, or acquired disorders.

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In a normal pregnancy, the plasma volume increases by approximately 40% and the red cell mass by 25% resulting in a hypervolemia ...

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