Trauma in Pregnancy

Daniel W. Robinson

Andrew N. Hogan

OVERVIEW

Three to eight percent of women will experience trauma while pregnant.¹^,²^,³ The true incidence of trauma in pregnancy is unknown, however, as the majority only involve minor injuries that do not prompt women to seek medical attention.⁴ Trauma is the leading nonobstetric cause of maternal death.²^,⁵ Anatomic and physiologic changes during pregnancy complicate the management of trauma in pregnant patients and place both mother and fetus at increased risk. Knowledge of this altered anatomy and physiology as well as a systematic approach to managing traumatic injuries are essential for providing optimal care to pregnant women. Additional consideration must be given to the fetus, whose outcome is directly related to both maternal well-being and gestational age.

Pregnancy itself increases a woman’s risk of suffering a traumatic injury because rates of interpersonal violence increase during pregnancy, with assaults often being aimed at the uterus.⁶ Maternal risk factors for trauma include improper seatbelt use, substance abuse, low socioeconomic status, age less than 20 years, and personal history of intimate partner violence (IPV).⁵^,⁶ Although pregnant women are susceptible to the same injuries as nonpregnant individuals, certain types of trauma are more prevalent. The most common causes of maternal trauma are motor vehicle collisions (MVCs), falls, and physical assault.⁷ Homicide accounts for a disproportionately larger percentage (57%-63%) of maternal deaths from trauma, while motor vehicle accidents make up much of the remainder.⁸

Minor trauma can result in complications such as placental abruption, preterm labor, spontaneous abortion, uterine rupture, cesarean section delivery, or fetal demise.²^,⁹ Reported rates of fetal loss after trauma vary widely, from less than 1% to 19.1%.¹⁰ The likelihood of a poor fetal outcome increases with the severity of maternal injuries. Maternal mortality is highly dependent on the circumstances and mechanism of injury, but overall rates are low.¹⁰

ANATOMY AND PHYSIOLOGY

Anatomic Changes in Pregnancy

Alterations in hormone secretion cause the uterus to grow from a small intrapelvic organ into a massive, highly perfused intra-abdominal organ that impinges upon the inferior aspect of the thoracic cavity. These anatomic changes are of special relevance during the examination and management of pregnant trauma patients.

During the first 12 weeks of pregnancy, the growing uterus remains below the pelvic brim. As it grows, it begins to displace other abdominal contents. The bladder, which sits anterior and
superior to the uterus in the nonpregnant state, is displaced in a cephalad direction. Outside the protective framework of the pelvis, the bladder becomes more susceptible to injury in trauma directed to the lower abdomen.³

Existing intra-abdominal contents, such as bowel and omentum, are displaced toward the superior aspect of the peritoneal cavity by the enlarging uterus. Compressive and disruptive forces are transmitted to adjacent structures in all directions. Anteriorly, increasing intra-abdominal pressure stretches the soft tissues of the abdominal wall. Distension of abdominal wall musculature alters baseline muscle tone and can mask the traditional peritonitic rigidity caused by intra-abdominal bleeding or leakage of gastrointestinal contents.⁶

As bowel and viscera are displaced into the upper abdomen, they exert pressure on the inferior diaphragm. This pressure displaces the diaphragm as much as 4 cm into the thoracic cavity, which leads to alterations in respiratory mechanics.¹¹ Bag mask ventilation of pregnant patients is typically more difficult, because increased intra-abdominal pressure adds resistance to diaphragmatic excursion during the inspiratory phase.

The intra-abdominal contents displaced by the uterus become concentrated into a smaller physical space at the superior pole of the peritoneal cavity. The gravid uterus occupies a relatively larger proportion of the abdominal space, exerting a protective influence over other intra-abdominal structures in blunt abdominal trauma.³ The uterus itself, however, is more susceptible to direct trauma at this stage. Furthermore, the organs concentrated in the space above the enlarged uterus are more vulnerable and more likely to be injured in penetrating trauma to the upper abdomen.¹²

By 20 weeks, the uterine fundus has reached the umbilicus. The uterus continues growing approximately one additional centimete with each subsequent week, and fundal height above the umbilicus can be used to estimate gestational age from this point on. Fundal height is a useful tool for determining fetal viability in unresponsive or unstable patients. The gestational age at which a fetus is considered viable (and thus eligible for full support) varies by institution, but is most commonly considered to be 24 weeks.

The average woman gains between 20 and 30 pounds (lbs) (9.1 and 13.6 kg) over the course of pregnancy due to uterine growth and other factors. Because this weight is concentrated in the abdomen, a corresponding shift in the maternal center of gravity also occurs. As a result, pregnant women are more prone to falls than their nonpregnant counterparts. Falls represent a very common mechanism of trauma during pregnancy, and extremity injuries are a frequent complication.¹³^,¹⁴

Physiologic Changes in Pregnancy

Cardiovascular

Progressive growth of the uterus and the fetoplacental unit causes a proportional increase in blood flow to the organ. Uterine perfusion at term represents a 10-fold increase (from 60 to 600 mL/min) compared to the nonpregnant state.³ With its upregulated perfusion and increased vascularity, the pregnant uterus can serve as a significant source of intra-abdominal bleeding in trauma.

Two physiologic compensatory mechanisms enable the maternal body to meet the increased demand for blood flow. First, maternal cardiac output increases roughly 1.5 L/min, driven primarily by an increase in maternal heart rate of 10 to 20 beats/min.¹¹ Second, maternal blood volume begins to increase around week 8 and rises nearly 50%, peaking in the early third trimester.¹¹ Plasma volume increases substantially more than red blood cell mass and causes a physiologic anemia (with hematocrit averaging 32%-34%) secondary to hemodilution.³

Increased levels of estrogen cause a decrease in vascular smooth muscle tone, which in turn reduces average systolic and diastolic blood pressures by 10 to 15 mm Hg.⁹ These alterations to maternal circulatory physiology can confound the assessment of shock in a traumatized pregnant patient. Traditional vital sign ranges are unreliable indicators of circulatory status in a pregnant woman. Increased plasma volume provides some degree of buffering against blood loss, but hypotension can develop rapidly and unexpectedly. Isotonic fluid and blood product requirements during resuscitation should be increased empirically to account for the presumed increase in intravascular volume. Alternative indicators of perfusion—mental status, mucous membrane hydration, skin temperature, skin color, and capillary refill—are helpful in determining volume status in such situations.³

Pregnancy causes significant changes in the distribution of maternal venous blood flow. Around week 20, when the uterine fundus is palpable at the umbilicus, the uterus has grown to reach the level of the inferior vena cava (IVC). Although the IVC is a retroperitoneal structure, it becomes susceptible to compression, or even occlusion, by the gravid uterus when the pregnant patient is in a supine position. Compression and occlusion of the IVC lead to decreased venous return to the right side of the heart, reduced preload, and ultimately a 30% reduction in cardiac output.¹ As a result of this decrease, systolic blood pressure drops up to 30 mm Hg, giving rise to the term supine hypotensive syndrome.³ Because the supine position is common during trauma resuscitations, special precautions need to be taken to relieve vena caval compression and avoid impairing hemodynamic stabilization. Placing rolled-up linens or a wedge under the patient’s right side and tilting 15° to 30° to the left allows gravity to displace the gravid uterus from the IVC.¹ The uterus can also be manually displaced to the patient’s left and held in position using a two-handed technique.

In addition to reduction in cardiac preload, vena caval obstruction leads to significant congestion in the venous networks that feed into the IVC. Typically, the venous circulation acts as a capacitance vessel and can accommodate this increased blood volume without complications. In situations of penetrating trauma to the pelvis or trauma to pelvic vessels from pelvic fractures, the increased pressure in the pelvic venous plexus can lead to life-threatening bleeding and even exsanguination.⁶ Similarly, injuries to the lower extremity may result in the unusually heavy venous bleeding.³

Respiratory

Oxygen consumption rises 20% during late pregnancy to meet the increased metabolic demand of the growing uterus and fetus.⁸ Simultaneously, the upward displacement of the diaphragm causes a decrease in functional residual capacity (FRC) of 10% to 25% between week 20 and term.¹⁵ This combination predisposes the pregnant patient to rapid desaturation when her respiratory mechanics or mental status is impaired by injury.¹⁵ Because the fetus is sensitive to hypoxemia, consider supplemental oxygen and endotracheal intubation early in the resuscitation of any pregnant trauma patient.

Pregnancy causes a variety of physiologic changes complicating intubation. Fluid shifts lead to edematous and hyperemic pharyngeal mucosa that is friable and prone to bleeding. Edematous pharyngeal tissues also contribute to worsening Mallampati scores in late pregnancy and more difficult vocal cord visualization during direct laryngoscopy.⁸ A smaller endotracheal tube than usual may be needed for a given patient during pregnancy.

Progesterone causes delayed gastric emptying in pregnancy, and all pregnant patients should be assumed to have a full stomach during resuscitation.¹⁰ Elevated levels of estrogen cause the lower esophageal sphincter to relax. Together with esophageal displacement by the gravid uterus, sphincter relaxation exacerbates gastroesophageal reflux in pregnant women. Increased reflux, frequent nausea, and high likelihood of a full stomach predispose the pregnant patient to aspiration.

Progesterone leads to an increase in minute ventilation through effects on the hypothalamus.³ This adaptation is mediated almost entirely by an increase in tidal volume, while the respiratory rate remains essentially unchanged compared to the nonpregnant state. The increase in minute ventilation leads to respiratory alkalosis and baseline hypocapnia. To compensate, the body maintains a normal pH range by increased renal bicarbonate excretion.¹⁵ During a resuscitation, end-tidal CO₂ readings in the typical range of 35 to 40 mm Hg actually represent relative hypoventilation and respiratory acidosis.

MECHANISMS OF TRAUMA

Blunt Trauma

Blunt trauma accounts for the majority of injuries among pregnant women. Pregnant women sustain blunt abdominal injuries more frequently than their nonpregnant counterparts due to the prominence of the gravid abdomen. Among pregnant patients who undergo medical evaluation after trauma, MVCs account for more than 50% of injuries. Falls and violent assault (by blunt
instruments) account for most of the remainder of traumas.³^,⁵ An estimated 30% of women will fall at least once during pregnancy, with most incidents occurring during the third trimester.⁴ Maternal mortality from blunt trauma is roughly 7%.¹¹ Splenic injury and retroperitoneal bleeding occur at increased rates.⁶ The gravid uterus and the fetoplacental unit are at risk of serious injury, leading to maternal and fetal complications including placental abruption, uterine rupture, fetomaternal hemorrhage (FMH), fetal head injury, and disseminated intravascular coagulation (DIC).

Seatbelt use is a major modifiable risk factor for blunt traumatic injury during pregnancy. Pregnant trauma victims are twice as likely to suffer serious bleeding and three times as likely to suffer fetus loss if they are improperly restrained.¹⁶ All pregnant women should be educated on proper seatbelt placement. The shoulder belt should pass between the breasts and to the side of the gravid uterus; the lap belt should cross the tops of the thighs below the abdomen.³

Penetrating Trauma

Penetrating trauma accounts for 9% to 16% of traumatic injuries during pregnancy, most commonly from gunshot wounds and stabbings.¹² High-energy projectiles such as bullets generally cause more serious injuries than knives and other low-energy weapons.³ The severity and complications related to penetrating trauma in the pregnant woman vary greatly depending on injury location. As pregnancy advances, the uterus enlarges and shields other intra-abdominal contents from penetrating trauma to the lower abdomen. Visceral injury from penetrating trauma occurs in less than 40% of pregnant women compared to more than 80% of nonpregnant patients.³ Maternal mortality from these wounds is low.¹² Seventy percent of gunshot wounds to the pregnant abdomen cause fetal injury.³ The thickness of the uterine wall decreases with gestational age, increasing the likelihood of fetal injury. Fetal demise occurs in approximately 70% of these cases.¹^,³ Although the overall frequency of hollow viscus injury from penetrating abdominal trauma is lower in pregnancy, the subset of wounds to the upper abdomen is associated with higher frequency and complexity of bowel injuries due to cephalad displacement of the intestines.¹²

Management of penetrating injuries in pregnant women follows similar guidelines as in nonpregnant individuals. Unstable patients with violation of the peritoneum are generally taken to the operating room. In other cases, imaging studies and diagnostic procedures help guide the decision to operate or observe. Although most penetrating wounds of the abdomen merit urgent surgical intervention, a special case exists for patients with stable vital signs and anterior, subfundal entry wounds. If it can be confirmed that the penetrating projectile did not exit the posterior wall of the uterus, these patients may be observed in some selected cases.³ Early consultation with a trauma surgeon and an obstetrician is imperative for penetrating injuries to the abdomen. Tetanus and antibiotic prophylaxis are recommended in most cases.¹

Interpersonal Violence

Women are at increased risk of IPV during pregnancy.¹⁷ Approximately 22% of pregnant women in the United States and 30% globally are victims of physical violence inflicted by an intimate partner.¹⁸^,¹⁹ IPV negatively impacts the short- and long-term well-being of both mother and fetus independent of the complications from associated traumatic injuries. Mothers are at increased risk of depression and suicide, while their unborn fetuses face an increased risk of preterm birth, premature rupture of membranes, abruption, and death.³^,²⁰

Universal screening for IPV is recommended for all pregnant trauma patients.²¹ Physicians should screen for IPV indicators such as depression, self-harm, suicidal ideation or attempts, inconsistent traumatic injuries, dominating partners, support system isolation, frequent visits to the healthcare system, and/or substance abuse.²⁰ Physical assault is commonly directed toward the abdomen, though the face, breasts, and head are also frequent targets.⁸^,⁶ Traumatic injuries can occur by both blunt and penetrating mechanisms.

Women with traumatic injuries from IPV are at risk of continued harm upon discharge. Before hospital discharge they should be offered information on resources for IPV victims. Although some institutions may have access to more robust resources than others, acute care providers should
be familiar with the options in their area. Involving social workers, if possible, can be useful in such situations. Some options for referral include women’s shelters, advocacy groups, law enforcement programs, or IPV hotlines. Obstetricians practicing at the evaluating institution or in the local outpatient setting may know of additional resources.

COMPLICATIONS OF TRAUMATIC INJURY

Placental Injury

Placental abruption occurs when the placenta separates from the uterine wall and damages the vasculature linking fetus and mother. This separation occurs when a traumatic force creates a shearing effect at the interface of the elastic uterine myometrium and inelastic placenta.¹ After maternal death, placental abruption is the second most common cause of fetal demise from trauma.³^,¹¹ Abruption occurs in 1% to 5% of minor trauma and between 20% and 50% of major trauma.³ Because imaging modalities such as ultrasound and computed tomography (CT) are not reliable for detecting abruption, clinical diagnosis remains the most dependable method. Premature contractions, uterine tenderness, and vaginal bleeding are signs of possible abruption. Cardiotocographic monitoring (CTM) is universally indicated to screen for fetal distress and possible abruption after trauma in pregnant women. Abruption may lead to complications such as fetomaternal hemorrhage (FMH), fetal exsanguination, and disseminated intravascular coagulation (DIC).

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