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INTRODUCTION AND EPIDEMIOLOGY
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Trauma remains the leading cause of nonobstetric morbidity and mortality in pregnant women.1 The severity of maternal injuries may be a poor predictor of fetal distress and outcome after a traumatic event (even minor ones). Trauma during pregnancy is associated with an increased risk of preterm labor, placental abruption, fetomaternal hemorrhage, and pregnancy loss. Achieving successful outcomes for both mother and fetus requires a collaborative effort by the prehospital provider, emergency physician, trauma surgeon, obstetrician, and neonatologist.
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Trauma during pregnancy is common. One study estimated that 32,810 pregnant women sustain injuries in motor vehicle crashes every year in the United States, a rate of 9 per 1000 live births.2 Motor vehicle crashes are the most common cause of blunt abdominal trauma, accounting for up to 70% of acute injuries. This is followed by falls and direct assault in decreasing order of frequency.3 The incidence of falls appears to increase with the advancement of pregnancy, presumably due to alterations in maternal balance and coordination. Penetrating injuries are less common than blunt trauma during pregnancy.
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PHYSIOLOGY OF PREGNANCY
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Physiologic changes in pregnancy are discussed in detail in chapter 25, "Resuscitation in Pregnancy." In addition to normal physiologic changes, conditions such as pregnancy-induced hypertension, placenta previa, pre-eclampsia, and eclampsia may significantly alter the presentation and complicate evaluation and treatment in the setting of trauma (see chapter 100, "Maternal Emergencies after 20 Weeks of Pregnancy and in the Postpartum Period").
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Table 25-1 summarizes important physiologic changes in pregnancy that affect resuscitation. Maternal blood volume expands at approximately week 10 of gestation and peaks at about a 45% increase from baseline at week 28. Because plasma volume increases more than red cell mass, mild physiologic anemia may be evident. Cardiac output increases by 1.0 to 1.5 L/min at week 10 of pregnancy and remains elevated until the end of pregnancy. Heart rate in the mother is generally increased by 10 to 20 beats/min in the second trimester, accompanied by decreases in systolic and diastolic blood pressures of 10 to 15 mm Hg.
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The relative hypervolemic state can mislead the clinician during maternal resuscitation after trauma and make clinical findings difficult to interpret. A pregnant patient may lose 30% to 35% of circulating blood volume before manifesting hypotension or clinical signs of shock. Uterine blood flow is directly proportional to maternal mean arterial pressure, so maintain and replace maternal blood volume aggressively and adequately.
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After week 12 of gestation, the uterus becomes an intra-abdominal organ, removing it from the relative protection of the maternal pelvis and making it susceptible to direct injury. The bladder moves anteriorly into the abdomen in the third trimester of pregnancy, increasing its vulnerability to injury. Uterine blood flow may increase to upward of 600 mL/min; severe maternal hemorrhage from uterine injury enters the equation at this ...