Trauma in Pregnancy

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Chapter 37

Trauma in Pregnancy


Trauma occurs in 6 to 7% of all pregnancies. It is the leading nonobstetric cause of maternal death, accounting for close to 50% of fatalities in pregnant women.1 The most common causes of injury in pregnancy, in order of frequency, that result in emergency department (ED) visits are motor vehicle collisions (MVCs), interpersonal violence, and falls.25 Patients with penetrating injuries are seen more frequently in EDs in inner city medical centers.6 Of note, 8% of women aged 15 to 40 admitted to a trauma center do not yet know they are pregnant.7 Commonly used thresholds of fetal viability are an estimated gestational age of 24 to 26 weeks or an estimated fetal weight of 500 g. Only viable fetuses are monitored, because no obstetric intervention will alter the outcome with a previable fetus.8 Counseling on proper seatbelt and alcohol use and screening for interpersonal violence may help to reduce the morbidity and mortality rates for pregnant patients. Although the essential principles of trauma management remain unchanged in the pregnant patient, a number of special points need to be considered. Pregnancy causes alterations in physiology and anatomy that affect multiple organ systems. Although there are two lives involved, maternal life takes priority.

Principles of Disease—Changes of Pregnancy



The normal cardiovascular changes of pregnancy can alter the presentation of shock and vascular events (Table 37-1).

Table 37-1

Hemodynamic Changes of Pregnancy (Mean Values)


Data from de Swiet M: The cardiovascular system. In Hytten F, Chamberlain G, eds: Clinical Physiology in Obstetrics. Oxford, UK: Blackwell Scientific Publications, 1980, pp 3-42; Colditz RB, Josey WE: Central venous pressure in supine position during normal pregnancy. Comparative determinations during first, second and third trimesters. Obstet Gynecol 36:769, 1970; Letsky E: The haematological system. In Hytten RF, Chamberlin G, eds: Clinical Physiology in Obstetrics. Oxford, UK: Blackwell Scientific Publications, 1980, pp 43-78; and Cruikshank DP: Anatomic and physiologic alterations of pregnancy that modify the response to trauma. In Buchsbaum HJ, ed: Trauma in Pregnancy. Philadelphia: WB Saunders, 1979, pp 21-39.

Some Alterations Mimic Shock.: Blood pressure declines in the first trimester, levels out in the second trimester, and then returns to nonpregnant levels during the third trimester. The decline in systole is small, 2 to 4 mm Hg, whereas diastole falls 5 to 15 mm Hg. Heart rate increases in pregnancy but does not rise by more than 10 to 15 beats per minute above baseline (mean of approximately 90 beats/min).

A major contributor to maternal hypotension is the supine hypotensive syndrome. After 20 weeks’ gestation, the uterus has risen to the level of the inferior vena cava, resulting in compression when the mother is supine. Such caval obstruction diminishes cardiac preload, which can decrease cardiac output by as much as 28%, resulting in reduced systolic blood pressure by 30 mm Hg. In late pregnancy, it is common for the inferior vena cava to become completely occluded when the pregnant patient is supine. Attempts at resuscitation will be improved if compression is relieved. In determining whether observed hypotension is related to positioning, the pregnant woman’s pelvis can be tilted so that the uterus is displaced from the inferior vena cava, (i.e, tilt the patient onto her left side unless otherwise prevented because of other injuries). The uterus can also be manually pushed to the left by with two hands, pushing the uterus toward the patient’s head. One early study found that tilting limited to only about 15 degrees may only partially resolve vena caval obstruction9; thus, maintaining a position between 15 and 30 degrees is optimal. Elevating the patient’s legs, where blood may pool owing to increased capacitance, will improve venous return.

Similarly, central venous pressure (CVP) measurements can be lowered in the last two trimesters by inferior vena caval compression. Normal CVP during pregnancy is approximately 12 mm Hg.

Some Alterations Can Exacerbate Traumatic Bleeding.: By the beginning of the second trimester and throughout the remaining pregnancy, cardiac output is increased 40%, to 6 L/min. Blood flow to the uterus increases from 60 mL/min before pregnancy to 600 mL/min at term. This hyperdynamic state is needed to maintain adequate oxygen delivery to the fetus. Because the mother’s total circulating blood volume flows through the uterus every 8 to 11 minutes at term, this organ can be a major source of blood loss when injured. By the third trimester, there is also marked venous congestion in the pelvis and lower extremities, increasing the potential for hemorrhage from both bony and soft tissue pelvic injuries.

Compression of the lower abdominal venous system by the gravid uterus increases peripheral venous pressure and volume in the legs, creating the potential for brisk blood loss from leg wounds. This alteration can play an important role in procedures that may be necessary for maternal resuscitation, such as central venous catheter placement.


The pregnant woman at term has a significantly reduced oxygen reserve. This effect comes from a reduction in functional residual capacity caused by diaphragm elevation and an increase in oxygen consumption related to the growing fetus, uterus, and placenta. In a classic study, Archer and Marx observed that mean arterial oxygen tension dropped by 29% in pregnant women at term during 60 seconds of apnea but just 11% in nonpregnant women. Labor accelerates this decline by a further 7%.10 In addition, minute ventilation increases, leading to hypocapnea. Therefore an arterial partial pressure of carbon dioxide (PaCO2) of 35 to 40 mm Hg may indicate inadequate ventilation and impending respiratory decompensation in the pregnant patient. At signs of respiratory compromise or hypoxia, endotracheal intubation should be considered, as maternal hypoxia rapidly leads to fetal hypoxia, distress, and possibly demise. There are no contraindications to rapid sequence intubation during pregnancy. Bag-valve-mask ventilation is more difficult in the pregnant patient.

Anatomic Changes in Pregnancy

The uterus remains an intrapelvic organ until approximately the 12th week of gestation. It reaches the umbilicus by 20 weeks and the costal margins by 34 to 36 weeks. It grows from a 7-cm, 70-g organ to a 36-cm, 1000-g structure at term. As a result of this growing mass, the normal anatomic location and function of multiple structures are altered.

The diaphragm progressively rises in pregnancy, with compensatory flaring of the ribs. Pneumothorax may be exacerbated and tension pneumothorax can develop more quickly in pregnancy because of this diaphragm elevation, combined with pulmonary hyperventilation. For thoracostomies done in the third trimester, the chest tube should be placed one or two interspaces higher than the usual fifth interspace site to allow for diaphragm elevation.

Abdominal viscera are pushed upward by the enlarging uterus, resulting in altered pain location patterns. The gravid uterus itself tends to protect abdominal organs from trauma but substantially increases the likelihood of bowel injury with penetrating trauma to the upper abdomen. Conversely, the upward displacement of the bowel makes it less susceptible to blunt trauma. The stretching of the abdominal wall modifies the normal response to peritoneal irritation. Therefore expected muscle guarding and rebound can be progressively blunted as pregnancy approaches term, despite significant intra-abdominal bleeding and organ injury, another factor that may lead to underestimation of the extent and gravity of maternal trauma.

In the first trimester, the bony pelvis shields the uterus. After the third month, the uterus rises out of the pelvis and becomes vulnerable to direct injury. The bladder is also displaced into the abdominal cavity beyond 12 weeks’ gestation, thereby becoming more vulnerable to injury. Like the uterus, the bladder becomes hyperemic, and injury may lead to a marked increase in blood loss compared with similar injury in a nonpregnant patient.

Imaging studies may show ureteral dilation that can be physiologic secondary to smooth muscle relaxation or caused by compression from the gravid uterus. Thus hydronephrosis is not necessarily pathologic. The ligaments of the symphysis pubis and sacroiliac joints are loosened during pregnancy. As a result, a baseline diastasis of the pubic symphysis may exist that can be mistaken for pelvic disruption on a radiograph.

Changes in Laboratory Values with Pregnancy

The physiologic anemia of pregnancy, resulting from a 48 to 58% increase in plasma volume and only an 18% increase in red blood cells, causes hematocrits of 32 to 34% by the 32nd to 34th week. Despite the lower hematocrit, there is actually an overall increase in oxygen-carrying capacity because of an increased total red blood cell mass.

Placental progesterone directly stimulates the medullary respiratory center, producing a PaCO2 of 30 mm Hg from the second trimester until term. The subsequent compensatory lowering of serum bicarbonate slightly reduces blood-buffering capacity for stress situations. A PaCO2 of 40 mm Hg in the latter half of pregnancy reflects inadequate ventilation and potential respiratory acidosis that could precipitate fetal distress.

Electrocardiographic changes include a left-axis shift averaging 15 degrees, caused by diaphragm elevation. Consequently, flattened T waves or Q waves in leads III and augmented voltage unipolar left limb lead may be seen.

Clinical Features of Trauma in Pregnancy

Blunt and Penetrating Trauma

The findings of the physical examination in the pregnant woman with blunt trauma are not reliable in predicting adverse obstetric outcomes. However, risk factors that are significantly predictive of contractions or preterm labor include gestational age greater than 35 weeks, assaults, and pedestrian collisions. In gravid patients, penetrating trauma of the abdomen has an increased likelihood of causing injuries of the bowel, liver, or spleen.

Fetal mortality rates range from 4 to 40% after maternal trauma, with most likely causes of fetal death occurring from placental abruption, maternal shock, and maternal death, in order of decreasing incidence.11 Risk factors significantly predictive of fetal death include ejections, motorcycle and pedestrian collisions, maternal death, maternal tachycardia, abnormal fetal heart rate, lack of restraints, and an Injury Severity Score greater than 9.8

Unbelted or improperly restrained pregnant women are twice as likely to experience excessive maternal bleeding, and fetal death is three times more likely to occur.11–13 For low- to moderate-severity crashes (constituting 95% of all MVCs), proper restraint use, with or without air bag deployment, generally leads to acceptable fetal outcomes. For high-severity crashes, even proper restraint does not improve fetal outcome.14

Pregnant crash-test-dummy trials show that improper placement of the lap belt over the pregnant abdomen causes a threefold to fourfold increase in force transmission through the uterus. The lowest force transmission readings through the uterus occur when a three-point seat belt is used properly. For correct position, the lap belt should be placed under the gravid abdomen, snugly over the thighs, with the shoulder harness off to the side of the uterus, between the breasts and over the midline of the clavicle.15 Women who receive information on seat belt use during pregnancy from a health care worker are statistically more likely to use seat belts and to use them properly than uninformed controls.15

Interpersonal Violence

Although it has been previously documented that intimate partner violence against women affects one in four U.S. women, and numerous health consequences have been associated with being a victim of such violence, a 2006 study by Silverman and colleagues conclusively demonstrated that physical abuse from husbands or boyfriends compromises a woman’s health during pregnancy, as well as her likelihood of carrying a child to term and the health of her newborn.16 Women experiencing abuse in the year before or during a pregnancy were 40 to 60% more likely than nonabused women to report high blood pressure, vaginal bleeding, severe nausea, kidney or urinary tract infections, and hospitalization during that pregnancy. Abused pregnant women were 37% more likely to deliver preterm, and children of abused pregnant women were 17% more likely to be born underweight. These conditions pose grave health risks to newborns, and children born to abused mothers were over 30% more likely than other children to require intensive care at birth.1618 Physicians detect only a minority of cases, which supports the need for routine screening for interpersonal violence in pregnant patients.


Falls become more prevalent after the 20th week of pregnancy.2 Protuberance of the abdomen, loosening of pelvic ligaments, strain on the lower back, and fatigability contribute to this problem. In a given pregnancy, about 2% of pregnant women sustain repeated direct blows to the abdomen because of falling more than once. Although repeated falls often trigger premature contractions, they seldom result in immediate labor and delivery.

Fetal Injury

Pregnancy does not alter rates of maternal mortality caused by trauma. However, trauma is associated with a high risk of fetal loss. When the mother sustains a severe level of injury, poor fetal outcome is predicted by maternal hypotension and acidosis (hypoxia, lowered pH, lowered bicarbonate) and a fetal heart rate of less than 110 beats/min.5,6,20 When the mother sustains life-threatening injuries, there is a 40% chance of fetal demise, compared with a less than 2% chance in cases of non–life-threatening maternal injuries. Maternal age and gestational age may also be important factors in determining fetal outcome.21

Maternal disseminated intravascular coagulation (DIC), which may be caused by placental products entering the maternal circulation, is a significant predictor of fetal mortality.11 For women with less severe trauma, fetal outcome is not predicted by maternal vital signs, abdominal tenderness, blood tests, or ultrasonography (US) results. Only cardiotocographic monitoring for a minimum of 4 hours is useful in predicting fetal outcome.3

Fatal in utero fetal injuries from blunt trauma usually involve intracranial hemorrhage and skull fractures. Such head injury is often secondary to fractured maternal pelvic bones striking the fetal skull as a result of vertex lie. Pelvic and acetabular fractures during pregnancy are associated with a high maternal (9%) and a higher fetal (38%) mortality rate.22 With penetrating trauma, gunshot wounds to the uterus are associated with a high incidence of fetal injury and fetal mortality. Stab wounds to the uterus produce substantial morbidity and mortality to the fetus.11

Placental Injury

In blunt trauma, 50 to 70% of all fetal losses result from placental abruption.19,23 It is the leading cause of fetal death after blunt trauma.

Placental separation results when the inelastic placenta shears away from the elastic uterus during sudden deformation of the uterus. Because deceleration forces can be as damaging to the placenta as direct uterine trauma, abruption can occur with little or no external sign of injury to the abdominal wall. Because all gas exchange between the mother and fetus occurs across the placenta, abruption inhibits the flow of oxygen to the fetus and causes in utero carbon dioxide (CO2) accumulation. Such hypoxia and acidosis can lead to fetal distress. Sustained uterine contractions induced by intrauterine hemorrhage also inhibit uterine blood flow, further contributing to fetal hypoxia.24

The diagnosis of abruption is a clinical one, and US and the Kleihauer-Betke test are of limited value.24 Classic clinical findings of abruption may include vaginal bleeding, abdominal cramps, uterine tenderness, maternal hypovolemia (up to 2 L of blood can accumulate in the gravid uterus), or a change in the fetal heart rate. However, many cases of placental abruption after trauma show no evidence of vaginal bleeding.11

The most sensitive indicator of placental abruption is fetal distress. Therefore prompt fetal monitoring is a very important assessment technique in trauma during pregnancy. There is also a close linkage of abruption to uterine activity, with increased frequency of contractions associated with abruption. US is less than 50% accurate as a first-line test in detecting placental abruption.19,25 If the abruption bleeds externally, not enough blood collects to be seen sonographically. Even with significant intrauterine blood accumulation, accurate US diagnosis may be difficult because of placental position (i.e., posterior) and confounding uterine or placental structural conditions.

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