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Trauma remains the leading cause of nonobstetric morbidity and mortality in pregnant women. After traumatic events (particularly apparently minor ones), the severity of maternal injuries may be a poor predictor of fetal distress and outcome. Trauma during pregnancy is associated with an increased risk of preterm labor, abruptio placentae, 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 U.S., a rate of 9 per 1000 live births.1

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The most common cause of blunt abdominal trauma is motor vehicle collisions, which account for up to 70% of acute injuries. This is followed by falls and direct assault in decreasing order of frequency.2 The incidence of falls appears to increase with the advancement of pregnancy, presumably due to alterations in maternal balance and coordination. Even minor abdominal trauma can result in fetal demise. Penetrating injuries are less common than blunt trauma during pregnancy.

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Physiologic changes in pregnancy are discussed in detail in Chapter 103, Normal Pregnancy. In addition to the normal physiologic changes associated with pregnancy, non–trauma-related complications of pregnancy must be considered. Conditions such as pregnancy-induced hypertension, placenta previa, preeclampsia, and eclampsia may significantly alter the presentation and complicate evaluation and treatment in the setting of trauma (see Chapter 104, Emergencies after 20 Weeks of Pregnancy and the Postpartum Period).

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Maternal blood volume begins to expand at approximately week 10 of gestation and peaks at about a 45% increase from baseline at week 28, which results in hypervolemia. Red cell mass increases to a lesser extent, which leads to the relative physiologic anemia of pregnancy. Cardiac output is increased 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 arteries constrict, which results in diminished fetal blood flow and tissue oxygenation before significant evidence of maternal hypovolemia appears.

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After week 12 of gestation, the uterus becomes an intra-abdominal organ, which removes it from the relative protection of the maternal pelvis and makes it more susceptible to direct injuries. The bladder also moves anteriorly into the abdomen in the third trimester of pregnancy, which increases its vulnerability. Uterine blood flow may increase to upward of 600 mL/min, so that severe maternal hemorrhage from uterine ...

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