The incidence of trauma related injuries during pregnancy has increased dramatically over the past 25 years¹ and is now the leading cause of nonobstetrical maternal death in the United States.² Adverse fetal outcomes include preterm delivery, low birthweight, and fetal demise.³

The severity of trauma does not always predict the severity of injury to mother and fetus, but major trauma is associated with a 40–50% risk of fetal death.⁴ Minor trauma, encompassing lower energy mechanisms, occurs much more frequently but still carries significant risk to the fetus. A Tennessee study identified 5352 expectant mothers and classified their injuries as major if hospital admission was required or minor if only emergency room evaluation occurred.⁴ They found that women in their first or second trimester with minor injury were 1.19 times more likely to have a child with prematurity or low birth weight.

Trauma complicates an estimated 1 in 12 pregnancies,¹ and 0.4% of pregnant women require hospitalization for their injuries.⁵ Motor vehicle crashes account for 50% of all traumatic injuries during pregnancy and 82% of trauma-related fetal deaths.⁶ A major risk factor is improper use of a seatbelt.⁷ Correct placement has the lap belt underneath the abdominal dome, decreasing the pressure transmitted across the uterus in a motor vehicle crash. The shoulder harness should overly the clavicle and run between the breasts. Sadly, this information is often overlooked during prenatal counseling.

Pregnancy makes women more prone to falls due to inherent changes such as increased joint laxity, weight gain, and dynamic postural stability.⁸ It is estimated that 1 in 4 will fall at least once during their pregnancy.⁹ Schiff found that 79% of pregnant women hospitalized after a fall were in their third trimester, and the most common injury was fracture in a lower extremity.¹⁰ The study also showed an 8-fold increase in placental abruption, a 4.4-fold increase in preterm labor, a 2.1-fold increase in fetal distress, and a 2.9-fold increase in fetal hypoxia.

Literature on thermal injuries and pregnancy is limited to case reports and series. Extensive burns cause significant physiologic stress, putting both the mother and fetus at risk. It is estimated that once the total body surface area of a burn exceeds 40%, the risk of mortality for the mother and fetus approaches 100%.¹¹

Intentional trauma is divided into two categories including assault by another person and self-inflicted injuries. Intimate partner violence (IPV) is the most common form of intentional trauma and carries significant risk to both the mother and fetus. The risk of preterm birth nearly triples and low birth weight increases 5.3-fold with such trauma.¹² The prevalence of domestic violence involving pregnant women that results in serious injury has been estimated between 10 and 30%.¹³ Risk factors associated with IPV include maternal or intimate partner substance abuse, low socioeconomic status, low maternal education level, unintended pregnancy, history of domestic violence prior to pregnancy, history of witnessed violence as a child, and unmarried status.¹⁴ The abdomen is the most common target associated with assault,¹⁵ increasing the likelihood of an intra-abdominal injury and fetal morbidity and mortality. The American College of Obstetricians and Gynecologists (ACOG) recommends universal screening of all pregnant women regarding IPV, and any pregnant woman who presents with a vague or suspicious history of trauma should raise the concern of battery.¹⁵ Warning signs include frequent office or emergency room visits, depression, substance abuse, discrepancy between injuries and given history, and a partner’s insistence on being present for the interview and examination.¹⁶ Questions regarding Intimate Partner Screening from ACOG are provided in Table 37-1.¹⁷

Suicide accounts for approximately 20% of all postpartum maternal deaths.¹⁸ Major risk factors include depression, substance abuse, history of domestic violence, and fetal or child death. Substance abuse is the best identifier for detecting women at risk,¹⁹ and a history of domestic violence or IPV has been associated in up to 54% of suicide cases among pregnant women.^20,21 Unsuccessful suicide attempts put the pregnant mother at risk for premature labor, cesarean delivery, need for transfusion, the respiratory distress syndrome, and low birthweight infants.^14,19

Understanding the many anatomic and physiologic changes that occur with pregnancy (Table 37-2) will help the treating physician better manage the mother and the fetus. The most obvious change seen in pregnancy is uterine growth. Figure 37-1 illustrates the uterine position throughout pregnancy. At 12 weeks of gestation, the uterus becomes an intra-abdominal organ as it rises above the pelvic brim. At 20 weeks, the top of the uterus is at the level of the umbilicus and, at 36 weeks, it reaches the costal margin. Toward the end of pregnancy, the fetal head drops back into the pelvis, lowering the fundal height. This descent makes the fetal head more susceptible to injury, particularly if the mother suffers a pelvic fracture.¹⁶ Uterine growth also shifts the maternal organs within the abdominal cavity, altering the typical findings on a physical examination and x-rays.

Cardiovascular System

The growing fetus requires a marked increase in oxygen delivery from the mother, and increased oxygen carrying capacity, cardiac output and minute ventilation augment this. The maternal plasma volume begins to increase at 10 weeks gestation and expands by 45% at full-term, while the red blood cell volume only increases by 18–30%.²² The disproportionate increase in plasma compared to red blood cells is protective as the mother will lose a large amount of blood during delivery. A higher plasma volume relative to red blood cell volume results in fewer lost red cells during hemorrhage. This physiologic anemia of pregnancy, with hematocrit falling to 32–34% at its nadir, occurs between the 30th and 34th week of gestation. Importantly, the extra blood volume may give a false sense of security for the treating physician because approximately 35% of maternal blood volume may be lost before any clinical signs of shock are observed.

During pregnancy, the normal blood pressure drops by 5–15 mm Hg, and the resting heart rate increases by 10–15 beats/min to increase cardiac output.²³ It is important not to attribute tachycardia or hypotension after trauma to physiologic changes associated with pregnancy without adequately evaluating for sources of hemorrhage. The uterine arteries supply the majority of blood to the fetus and are maximally dilated during pregnancy. Hypovolemia may cause vasoconstriction to divert blood to the mother’s vital organs, and this will significantly decrease the placental blood flow. Shunting of blood away from the placenta may manifest as fetal distress before systemic signs of hemorrhage are seen in the mother.

As the growing uterus displaces the diaphragm, it pushes the heart to the left and upward along its long axis, producing an enlarged cardiac silhouette on chest radiographs. Most pregnant women will have some degree of benign pericardial effusion, while an electrocardiogram will show only a slight left-axis deviation from the altered position of the heart.²⁴

During the middle of the second trimester, maternal position greatly affects cardiovascular physiology. While supine, the gravid uterus compresses the inferior vena cava leading to a decrease in venous return to the heart and a drop in the cardiac output by as much as 25%. The “supine hypotensive syndrome” leads to dizziness, pallor, tachycardia, diaphoresis, nausea, and hypotension. The uterus also compresses the aorta causing decreased blood flow to the uterus. With the uterine arteries maximally dilated during pregnancy, autonomic regulation is lost and blood flow is entirely dependent on maternal mean arterial pressure.²⁵ Placing the mother in the left lateral decubitus position restores venous flow and improves cardiac output.

Respiratory System

Both hormonal and mechanical changes in pregnancy contribute to increased minute ventilation. As the gravid uterus enlarges, it displaces the diaphragm approximately 4 cm, decreasing functional residual capacity. Elevated progesterone levels cause increased tidal volume and hyperventilation which augments minute ventilation, and it is common for a woman in her third trimester to have hypocapnia (PaCO₂ of 30 mm Hg) and a compensated respiratory alkalosis. It is important to recognize that a pregnant patient with a PaCO₂ of 35–40 mm Hg may be exhibiting signs of impending respiratory failure. The baseline hyperventilation of pregnancy also reduces the mother’s ability to compensate for metabolic acidosis.

Renal System

To compensate for the increased blood volume in pregnancy, the renal plasma flow and glomerular filtration rate (GFR) both increase. Paired with hemodilution from a 50% increase in plasma volume, the serum creatinine concentration decreases by an average of 0.4 mg/dL. In pregnancy, a normal creatinine ranges from 0.4 to 0.8 mg/dL.²⁶ The increased GFR leads to excretion of other metabolic products that may exceed the tubular reabsorption capability and result in proteinuria and glucosuria, also. As the uterus grows, it can cause partial ureteral obstruction and physiologic hydronephrosis, particularly in the late stages of gestation. The right side is more affected than the left, due to the cushioning of the left ureter by the sigmoid colon.²⁴

Coagulation System

Thrombosis in pregnancy is related to two components of Virchow’s triad—stasis and hypercoagulability. Stasis occurs as the uterus grows and compresses venous outflow; however, the risk of venous thromboembolic events is the same throughout all stages of pregnancy, suggesting that hypercoagulability is the more significant factor. Increased concentrations of clotting factors cause hypercoagulability in pregnancy and may protect the mother from hemorrhage at childbirth or miscarriage. Pregnant women are at higher risk of thromboembolic events, with a three- to fourfold increase in arterial thromboembolism and four- to fivefold increase in venous thromboembolism.²⁷ Of interest, deep venous thrombosis represents 80% and pulmonary embolus 20% of venous events. In pregnancy, deep venous thrombosis is more likely to be proximal, massive and on the left.²⁷

Gastrointestinal System

Nausea and vomiting are common in pregnancy. Gastric emptying is unchanged, but pregnant women are more susceptible to aspiration with anesthetics. Alterations in liver function tests include a mild generalized decrease of aspartate transaminase, alanine transaminase, gamma-glutamyl transpeptidase, and bilirubin.²⁸ Alkaline phosphatase activity increases, particularly in the third trimester, while serum albumin concentration decreases throughout pregnancy and can be as low as 3.0 g/dL in the third trimester. Total body albumin, however, is elevated because of hemodilution.²⁴ As the fetus grows, maternal nutrition needs to increase, so a pregnant patient who is to remain nil per os (NPO) for an extended period of time should receive total parenteral nutrition (TPN) with a goal of 36 kcal/kg/d.²⁹

The first priority in treating an injured pregnant patient is the mother as early and aggressive maternal resuscitation directly correlates with improved fetal outcomes.³⁰ Fetal mortality increases with the severity of maternal injuries and is more likely after direct fetoplacental injury, maternal shock, pelvic fracture, maternal injury to the brain, or hypoxia.²⁴ Preterm delivery is a significant risk, and a fetus delivered before 23 weeks is considered not viable.