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

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 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

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.

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).