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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.1,2 This is impractical because the normal blood loss is believed to be 300 to 600 mL following a vaginal delivery and 900 to 1200 mL following a cesarean section.3,4 Postpartum hemorrhage 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.1,3 A clinically useful definition is excessive bleeding that results in signs and/or symptoms of hypovolemia (e.g., dizziness, hypotension, oliguria, palpitations, syncope, shortness of breath, and tachycardia), which corresponds to a 10% or more loss in total blood volume.4 Postpartum hemorrhage can occur at sites within or external to the genitourinary tract (Table 166-1).

TABLE 166-1Anatomic Sites of Postpartum Hemorrhage

The incidence of postpartum hemorrhage ranges from 2% to 3% of pregnancies in the United States.5 The risk factors for postpartum hemorrhage are listed in Table 166-2. The etiologies are varied (Table 166-3 and Figure 166-1). Primary postpartum hemorrhage accounts for greater than 90% of all cases and occurs within 24 hours of delivery. Uterine atony (i.e., lack of uterine contraction) is by far the most common cause. This is often the result of excessive bleeding from the placental implantation site. Trauma (e.g., genital tract lacerations, surgical incisions, or uterine rupture) is the second most common etiology. Hemorrhage can be associated with a considerable drop in hematocrit before clinical symptoms occur and result in significant maternal complications.

TABLE 166-2Risk Factors for Postpartum Hemorrhage
TABLE 166-3Etiologic Associations for Postpartum Hemorrhage

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