Until about week 12 of gestation, the uterus is protected to a large degree by the bony structure of the maternal pelvis. As a result, direct fetal injury is relatively infrequent in blunt abdominal trauma during pregnancy. When fetal injuries do occur, they are typically seen in later gestation and tend to involve the fetal skull and brain. These injuries are frequently sustained in association with fractures to the maternal pelvis when the fetal head is engaged. When the uterus is penetrated by a sharp object or projectile, the fetus has a high probability of sustaining injury. 68
Uterine rupture is a relatively uncommon complication of blunt trauma sustained during pregnancy. Its incidence has been reported as 0.6 to 1.0 percent of injuries in pregnancy and is more likely to occur during the late second and third trimesters and when there is direct and forceful impact upon the uterus. 46 The fetal mortality rate in such cases is nearly 100 percent, whereas maternal mortality is less than 10 percent. The presentation of uterine rupture may be quite nonspecific, but loss of the palpable uterine contour, ease of palpation of fetal parts, or radiologic evidence of abnormal fetal location is suggestive of the diagnosis.
Uterine irritability and the onset of preterm labor may be precipitated by acute abdominal trauma during pregnancy. Numerous reports have noted the management of premature labor in pregnant trauma patients with tocolytic agents, but the use has not been generally recommended and requires individualization. 19 Tocolytic agents have numerous described adverse side effects, such as fetal and maternal tachycardia, which may complicate the evaluation of trauma patients. Additionally, their use may further impair the ability to diagnose other significant traumatic injuries, specifically placental abruption. If tocolytics are considered, an obstetrician should be consulted prior to administration.
Second only to maternal death, abruptio placentae is the most common cause of fetal death. Abruptio placentae complicates 1 to 5 percent of minor injuries during pregnancy and up to 40 to 50 percent of major traumas.16 Placental abruption has been described as being caused by the deformation of the elastic uterus around the relatively inelastic placenta. Further exacerbated by increased intrauterine pressures, shear forces are applied to the placental base, leading to separation from the uterine wall. Findings consistent with abruptio placentae include abdominal pain, vaginal bleeding, and tetanic uterine contractions. Placental abruption may also lead to the introduction of placental products into the maternal circulation, stimulating disseminated intravascular coagulation (DIC). The correlation and predictive value of DIC with respect to fetal mortality remains unsettled.71.?
The fetal and maternal circulations are normally separate during pregnancy, and fetal red blood cells may enter the maternal bloodstream in cases of traumatic injury. The incidence of such fetal-maternal hemorrhage in trauma during pregnancy is four to five times that which occurs in pregnancies not complicated by injury. 46 Fetal-maternal hemorrhage occurs in over 30 percent of significant trauma in pregnant patients and is implicated in the sensitization and subsequent isoimmunization of Rh-negative patients. As little as 0.1 to 0.3 mL of fetal cells is sufficient to sensitize 70 percent of Rh-negative women. 11 The fetal hemorrhage itself poses the direct risks of fetal hypovolemia, anemia, distress, and death. Anterior placental location appears to be associated with increased risk of fetal-maternal hemorrhage. 1
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