Chapter 21. Postpartum Hemorrhage & the Abnormal Puerperium

Essentials of Diagnosis

• Postpartum hemorrhage denotes excessive bleeding (>500 mL in vaginal delivery) following delivery. Hemorrhage may occur before, during, or after delivery of the placenta. Actual measured blood loss during uncomplicated vaginal deliveries averages 700 mL, and blood loss often may be underestimated. Nevertheless, the criterion of a 500-mL loss is acceptable on historical grounds.
• Blood lost during the first 24 hours after delivery is early postpartum hemorrhage; blood lost between 24 hours and 6 weeks after delivery is late postpartum hemorrhage.

Pathogenesis

The incidence of excessive blood loss following vaginal delivery is 5–8%. Postpartum hemorrhage is the most common cause of excessive blood loss in pregnancy, and most transfusions in pregnant women are performed to replace blood lost after delivery. Hemorrhage is the third leading cause of maternal mortality in the United States and is directly responsible for approximately one-sixth of maternal deaths. In less developed countries, hemorrhage is among the leading obstetric causes of maternal death.

Causes of postpartum hemorrhage include uterine atony, obstetric lacerations, retained placental tissue, and coagulation defects.

Uterine Atony

Postpartum bleeding is physiologically controlled by constriction of interlacing myometrial fibers that surround the blood vessels supplying the placental implantation site. Uterine atony exists when the myometrium cannot contract.

Atony is the most common cause of postpartum hemorrhage (50% of cases). Predisposing causes include excessive manipulation of the uterus, general anesthesia (particularly with halogenated compounds), uterine overdistention (twins or polyhydramnios), prolonged labor, grand multiparity, uterine leiomyomas, operative delivery and intrauterine manipulation, oxytocin induction or augmentation of labor, previous hemorrhage in the third stage, uterine infection, extravasation of blood into the myometrium (Couvelaire uterus), and intrinsic myometrial dysfunction.

Obstetric Lacerations

Excessive bleeding from an episiotomy, lacerations, or both causes approximately 20% of postpartum hemorrhages. Lacerations can involve the uterus, cervix, vagina, or vulva. They usually result from precipitous or uncontrolled delivery or operative delivery of a large infant; however, they may occur after any delivery. Laceration of blood vessels underneath the vaginal or vulvar epithelium results in hematomas. Bleeding is concealed and can be particularly dangerous because it may go unrecognized for several hours and become apparent only when shock occurs.

Episiotomies may cause excessive bleeding if they involve arteries or large varicosities, if the episiotomy is large, or if a delay occurred between episiotomy and delivery or between delivery and repair of the episiotomy.

Persistent bleeding (especially bright red) and a well-contracted, firm uterus suggest bleeding from a laceration or from the episiotomy. When cervical or vaginal lacerations are identified as the source of postpartum hemorrhage, repair is best performed with adequate anesthesia.

Spontaneous rupture of the uterus is rare. Risk factors for this complication include grand multiparity, malpresentation, previous uterine surgery, and oxytocin induction of labor. Rupture of ...