If the abdominal force associated with trauma is considerable, then the placenta can be torn or "fractured" (see Fig. 47-9). If so, then life-threatening fetal hemorrhage may be encountered either into the amnionic sac or by fetomaternal hemorrhage (Pritchard, 1991). he tear is linear or stellate and is caused by rapid deformation and reformation (Fig. 47-10). Especially if there is ABO compatibility, fetomaternal hemorrhage is quantified using a Kleihauer-Betke stain of maternal blood. A small amount of fetal-maternal bleeding has been described in up to a third of trauma cases, and in 90 percent of these, the volume is < 15 mL (Goodwin, 1990; Pearlman, 1990). Parenthetically, nontraumatic placental abruption is much less often associated with signifi minor injuries and up to 50 percent of major injuries (Pearlcant fetomaternal hemorrhage because only minimal fetal blood man, 1990; Schif, 2002). Abruption was found to be more enters into the intervillous space. With traumatic abruption, likely if vehicle speed exceeded 30 mph (Reis, 2000). however, massive fetomaternal hemorrhage may follow. In one Clinical indings with traumatic abruption may be simistudy, the risk of associated uterine contractions and preterm lar to those for spontaneous placental abruption (Chap. 41, labor was a 20-fold if there was evidence for a fetomaternal
FIGURE 47-10 A. Partial placental abruption in which the adherent blood clot has been removed. Note the laceration of the placenta (arrow), which caused fetal death from massive fetomaternal hemorrhage. B. Kleihauer-Betke stain of a peripheral smear of maternal blood.
The dark cells that constituted 4.5 percent of red blood cells are fetal in origin, whereas the empty cells are maternal.
bleed (Muench, 2004). With severe fetal bleeding, long-term adverse neurological outcomes are frequent (Kadooka, 2014).
Blunt trauma leads to uterine rupture in < 1 percent of severe cases (American College of Obstetricians and Gynecologists, 20 17b). Rupture is more likely in a previously scarred uterus and is usually associated with a direct impact of substantial force. Decelerative forces following a 25-mph collision can generate up to 500 mm Hg of intrauterine pressure in a properly restrained woman (Crosby, 1968). Clinical indings may be identical to those for placental abruption with an intact uterus, and maternal and fetal deterioration are soon inevitable. Pearlman and Cunningham (1996) described uterine fundal "blowout" with fetal decapitation in a 20-week pregnancy following a high-speed collision. Similarly, Weir and colleagues (2008) described supracervical uterine avulsion and fetal transection at 22 weeks. CT scanning may be useful to diagnose uterine rupture with a dead fetus or placental separation (Kopelman, 2013; Manriquez, 2010; Sadro, 2012).