A profuse hemorrhage occurring prior to or shortly after the birth of the child is always dangerous and not infrequently a fatal complication.
—J. Whitridge Williams (1903)
As in Williams’ time, obstetrical hemorrhage continues along with hypertension and infection to be one part of the infamous “triad” of maternal death causes. It also is a leading reason for admission of pregnant women to intensive care units (Chantry, 2015; Crozier, 2011; De Greve, 2016; Guntupalli, 2015). Hemorrhage was a direct cause of 11.4 percent of 5367 pregnancy-related maternal deaths from 2006 to 2013 in the United States (Creanga, 2015, 2017). Similarly, 16 percent of 1102 maternal deaths recorded in the Nationwide Inpatient Sample were caused by hemorrhage (Kuriya, 2016). In developing countries, hemorrhage’s contribution is even more striking, and it is the single most important cause of maternal death worldwide (Goffman, 2016; Oladapo, 2016; Thomas, 2016). Despite these numbers, a declining maternal mortality rate from hemorrhage in the United States has been a seminal achievement. But, as discussed in Chapter 1 (Maternal Mortality), it seems unlikely that deaths from hemorrhage have reached an irreducible minimum.
Mechanisms of Normal Hemostasis
A major concept in understanding the pathophysiology and management of obstetrical hemorrhage is the mechanism by which hemostasis is achieved after normal delivery. Recall that near term an incredible amount of blood—at least 600 mL/min—flows through the intervillous space (Pates, 2010). This prodigious flow circulates through the spiral arteries, which average 120 in number. Also, recall that these vessels have no muscular layer because of their remodeling by trophoblasts, which creates a low-pressure system. With placental separation, these vessels at the implantation site are avulsed, and hemostasis is achieved first by myometrial contraction, which compresses this formidable number of large vessels. Compression is followed by clotting and obliteration of vessel lumens.
If, after delivery, the myometrium contracts vigorously, fatal hemorrhage from the placental implantation site is unlikely. Importantly, an intact coagulation system is not necessary for postpartum hemostasis unless there are lacerations in the uterus, birth canal, or perineum. At the same time, however, fatal postpartum hemorrhage can result from uterine atony despite normal coagulation.
Traditionally, postpartum hemorrhage is defined as the loss of ≥500 mL of blood after completion of the third stage of labor. This is problematic because almost half of all women delivered vaginally shed that amount of blood or more when losses are carefully measured (Pritchard, 1962). These results are depicted in Figure 41-1 and show further that approximately 5 percent of women delivering vaginally lose more than 1000 mL of blood. According to the American College of Obstetricians and Gynecologists (2017d), postpartum hemorrhage is defined as ...