Although uncommon, fetal skull and brain injuries are more likely if the head is engaged and the maternal pelvis is fractured (Palmer, 1994). Conversely, fetal head injuries, presumably from a contrecoup efect, may be sustained in unengaged vertex or nonvertex presentations. Fetal skull fractures are rare and best seen using CT imaging (Sadro, 2012). One example is Figure 46-8 (p. 908). Other sequelae include intracranial hemorrhage (Gherman, 2014; Green-hompson, 2005). A newborn with paraplegia and contractures associated with a motor vehicle accident sustained several months before birth was described by Weyerts and colleagues (1992). Other injuries have included fetal decapitation or incomplete midabdominal fetal transection at midpregnancy (Rowe, 1996; Weir, 2008).
Catastrophic events that occur with blunt trauma include placental injuries-abruption or placental tears (Fig. 47-9). Placental separation from trauma is likely caused by deformation of the elastic myometrium around the relatively inelastic placenta (Crosby, 1968). his may result from a deceleration injury as the large uterus meets the immovable steering wheel or seat belt. Some degree of abruption complicates 1 to 6 percent of p. 768). Kettel and coworkers (1988) emphasized that traumatic abruption may be occult and unaccompanied by uterine pain, tenderness, or bleeding. In our experiences with 13 such women at Parkland Hospital, 11 had uterine tenderness, but only five had vaginal bleeding. Because traumatic abruption is more likely to be concealed and generate higher intrauterine pressures, associated coagulopathy is more likely than with nontraumatic abruption (Cunningham, 2015). Partial separation may also generate uterine activity, which is described more fully on page 930. Other features are evidence of fetal compromise such as fetal tachycardia, sinusoidal pattern, late decelerations, acidosis, and fetal death.
FIGURE 47-9 Mechanism of placental tear or "fracture" caused by a deformationreformation injury. Placental abruption is seen as blood collecting in the retroplacental space. Inset. From here, blood can be forced into placental bed venules and enter maternal circulation. Such fetomaternal hemorrhage may be identified with Kleihauer-Betke testing.