Abdominal Trauma in Pregnant Patients

Introduction

Diagnostic imaging of the pregnant trauma patient is among the most important and challenging clinical scenarios that emergency and trauma radiologists may encounter in their practice. With an estimated incidence of 5% to 7% across all pregnancies, trauma is both the leading cause of nonobstetric maternal mortality and a significant cause of fetal loss. Moreover, pregnant patients face a higher risk of suffering severe abdominal injuries than do nonpregnant patients due to the excellent perfusion of the uterus and placenta, as well as lack of room for soft-tissue distention, which increases the risk of injury to large veins. Blunt mechanisms of trauma are overwhelmingly more common than penetrating trauma, with motor vehicle collisions accounting for nearly 50% of cases. Falls (25%) and assaults including domestic violence (18%) also account for significant percentages of cases, while gunshot wounds, the most common cause of penetrating trauma, account for 4% of cases.

Pregnant patients are susceptible to the same spectrum of injuries as nonpregnant victims of trauma. While there is no evidence that serious traumatic injuries, taken together, are associated with a higher mortality rate during pregnancy, specific injuries such as pelvic and acetabular fractures are associated with increased maternal mortality due to increased blood flow to the pelvis, and the risk of secondary coagulopathy if amniotic fluid enters maternal circulation. Conversely, bowel injuries are less frequently reported among pregnant women in both blunt and penetrating trauma, presumably due to the protection conferred by the gravid uterus. When pregnant women die as a result of trauma, the most common causes are head injuries and hemorrhagic shock.

As the severity of the maternal injury increases, the risk of fetal loss rises commensurately, such that an Injury Severity Score (ISS) greater than 25 was associated with a fetal loss rate of 50% in one large study. In nearly all cases, maternal death leads to fetal death. In pregnant women who survive, placental abruption is the most common cause of pregnancy loss. Fetal loss can also occur following relatively minor maternal injuries, with cases of fetal death reported following insignificant trauma (i.e., ISS = 1).

Clinical Management of the Pregnant Trauma Patient

The management of the pregnant trauma patient begins with the standard techniques that would be used to care for any trauma patient, including attention to the airway, breathing, and circulation. The primary objective during the critical early management is maternal stabilization, given that maternal survival will optimize the chances of fetal survival. Pregnant women after 20 weeks of gestation should be placed in the 30-degree left lateral decubitus position, which helps avoid systemic hypotension due to compression of the aorta and inferior vena cava by the gravid uterus. As the emergency team evaluates a pregnant trauma patient, it is important to consider the normal physiologic changes of pregnancy, including increased blood volume, increased heart rate, and decreased systolic and diastolic blood pressure. Physiologic hypervolemia of pregnancy (with up to a 50% increase in total blood volume) and associated vasoconstriction may falsely indicate a stable hemodynamic state and may mask the typical signs of hemorrhage until a significant fraction of blood volume is lost. If classical signs and symptoms of hypovolemic shock are present (typically seen with blood loss of 15%–30% or class II hemorrhage), the rate of fetal mortality can reach up to 80%. A blood loss of 0% to 15% (class I hemorrhage) may be the best window for early intervention. Capillary filling time of more than 3 seconds may be an early indicator to assess signs of early hypovolemic shock, although it may be completely normal in patients in late pregnancy until they lose 15% of their blood volume.

Once the mother is stable, evaluation of the fetus can proceed. Bedside obstetric ultrasonography should be done early on to determine fetal heart condition, viability, gestational age, presentation, and amniotic fluid volume. For a viable pregnancy (i.e., fetal age between 22 and 24 weeks), continuous external fetal monitoring and tocometry are the most effective way to evaluate uterine activity and to identify signs of placental abruption, including fetal tachycardia or bradycardia, a nonreassuring fetal tracing, or fetal death. Pregnancies that are not viable, i.e., before 20 weeks of gestation, can be sufficiently assessed by intermittent Doppler auscultation of the fetal heart rate.

Imaging of the Pregnant Trauma Patient

General Principles

The potential benefits of imaging the pregnant trauma patient are threefold: (1) early diagnosis of maternal injuries to allow proactive and aggressive treatment of injuries, (2) avoidance of nonobstetric laparotomy to avoid the risk of preterm labor, and (3) guidance of surgical technique when necessary to address all known maternal injuries in an efficient and effective manner ( Fig. 7.1 ). To accomplish these goals, the initial imaging evaluation often requires a multimodal approach consisting of ultrasound, conventional radiography, computed tomography (CT), and angiography. While ultrasound is free of ionizing radiation, its value for detecting injuries, including active arterial bleeding, in pregnant women is limited. Therefore, conventional radiography and CT remain indispensable for imaging pregnant women in the setting of major trauma despite the use of ionizing radiation in these examinations. Magnetic resonance imaging (MRI), while considered safe during pregnancy, is typically not feasible or practical in the acute setting, given prolonged scanning times during which the patient will be removed from the acute care setting.