Fetal Trauma from Motor Vehicle Collisions

“Trauma is more likely to cause maternal death than any other medical complication of pregnancy.” 1

Six to seven percent of pregnant women experience trauma during pregnancy. When we’re responding to a pregnant woman who has experienced some form of trauma, two patients require our care: the mother and the fetus. EMS providers need to be aware of anatomical and physiological changes in pregnancy that can mask or mimic injury, which complicates assessment of the pregnant trauma patient.2

Although trauma is the leading cause of non-obstetric maternal death, less than one-half percent of pregnant women with traumatic injuries require hospitalization.2 Motor vehicle collisions are the leading cause of injury during pregnancy, accounting for 60% of injuries. Falls and physical abuse account for much of the remainder.2 Although any cause of blunt trauma—falls, physical abuse, collision—can have adverse impacts on the mother or fetus, motor vehicle collisions cause the most severe maternal injuries and fetal death.3

This article will review pregnancy anatomy and physiology, describe fetal trauma injuries, discuss assessment and treatment of maternal trauma, review components of fetal assessment and discuss strategies to prevent fetal trauma from motor vehicle collisions.

Pregnancy Anatomy

The uterus, a muscular organ, grows from a volume of 5 ml to 5 liters during pregnancy.4 In the first trimester, the uterus is still low in the abdomen and surrounded by the pelvis. In the second and third trimesters, it grows upward and outward, losing the protection of the pelvic ring and displacing other abdominal organs.4 The fetus is still relatively protected by the shock-absorbing properties of the amniotic fluid.4 The placenta is a vascular organ that exchanges nutrients and oxygen for metabolic waste with the fetus. The loose attachment of the placenta to the wall of the uterus is weaker than either of the two tissues.4

The gestation age of the fetus is split into three trimesters. From conception to the end of the first trimester, the pregnant woman experiences dramatic physical changes. Her blood volume increases, her breasts enlarge and she is often fatigued. Meanwhile, the fetus is growing to a weight of a few ounces, is moving spontaneously, and a heartbeat is audible with a Doppler ultrasound.5

During the second trimester, maternal blood volume has increased by 30%–40%. Cardiac output increases from one liter per minute to 6–7 liters per minute. One-sixth of maternal blood volume is in the placenta. Trauma that causes a placental laceration will lead to a quick and severe loss of blood.5 The mother is aware of fetal movement and experiences diminished agility from her shifting center of gravity and weight gain.

The expanding uterus grows into the peritoneal cavity after the 12th week of pregnancy. While the uterus is now more susceptible to injury, it offers some protection to other maternal organs, like the small intestine.2 The bladder is the most susceptible to damage from trauma since it is forced upward by the uterus.2, 5 The fetus is increasing in length and weight. By 20 weeks, the heartbeat can be auscultated with a stethoscope. Twenty- four to 25 weeks is considered the practical low-end age for out-of-uterus viability or survival.

The risk of accidental injury is greatest in the third trimester. Balance and coordination suffer greatly.2 This is when most falls and motor vehicle collisions occur. The fetus grows to its birth size and weight and is kicking actively.

Blood pressure does not change as significantly as once thought. A change of 2–4 mmHg for the systolic pressure and 5–15 mmHg for the diastolic pressure is normal. The mother’s resting heart rate increases by 10–15 beats per minute during pregnancy.2 Never discount tachycardia. During assessment, tachycardia and low blood pressure are not just caused by the pregnancy, but could be caused by blood loss.2

Maternal plasma volume increases by 50% during pregnancy, but red blood cell volume only increases by 18%–30%. Thus, the patient has relatively fewer red blood cells than normal and a diminished capacity to transport oxygen. Hematocrit, the percentage of red blood cells in total blood volume, averages 32%–34 % during pregnancy.2

Fetal Trauma

It is estimated that 1,500–5,000 fetal deaths each year result from maternal involvement in motor vehicle crashes.4 Estimates vary, since recent maternal involvement in a motor vehicle crash is not recorded on fetus death certificates. The rate of fetal death after blunt trauma is estimated between 3%–38%.3 Statistics do not include uncounted adverse outcomes from motor vehicle collisions, like:

  • Disabilities resulting from in-utero injuries.
  • Complications from emergency delivery, such as low birth weight or neonatal respiratory distress syndrome that lead to long-term negative outcomes.4 Low birth weight can lead to a lifetime of possible disabilities and medical problems.4 Neonatal respiratory distress syndrome means breathing difficulty for the neonate because the lungs are not fully developed.4

The direction of impact determines the pattern of injuries. A frontal collision involves an abrupt stop, causing the patient to collide with the windshield, airbag, dash and/or steering wheel. An unrestrained patient may be ejected. Common front collision injuries include: lower extremity fractures or dislocations, and head, c-spine, torso or blunt trauma.

During a side-impact collision, the patient is accelerated side to side or thrown across the vehicle. Common injuries include: pelvic fractures, pulmonary contusions, solid organ injury and diaphragmatic rupture.

In a rear-impact collision, the patient is accelerated forward. Back-and-forth, whiplash motion of the head makes the c-spine vulnerable to injury. Unrestrained occupants can also be ejected, which results in the most serious injuries.

An acceleration-deceleration collision causes adverse movement between two structures. For example, shear forces can rupture and tear the aortic arch and distal aorta, or the uterus and placenta.

The effect of trauma on the fetus depends on:6

  • Gestational age of the fetus
  • Type and severity of the trauma
  • Extent of disruption to normal uterine and fetal physiology.

Maternal and fetal survival is dependent on an open and functional airway. If the airway is not open or the patient is unable to breathe, fetal and maternal death will occur in minutes. Survival is also dependent on an adequate circulating blood volume perfusing the mother’s vital organs—brain, heart, lungs, liver and kidneys—and the placenta.

Because maternal survival is critical to fetal survival, the mother is the assessment and treatment priority.

The following factors are associated with fetal death after trauma:

  • Maternal death
  • Maternal hypotension (shock)
  • Severe maternal injury
  • Placental abruption
  • Maternal ejection from vehicle
  • Maternal pelvic fracture
  • Maternal history of smoking or alcohol use
  • Young maternal age.

Fetal death is most likely to result from placental abruption, maternal shock and maternal death.2, 3 The fetal mortality rate if the mother is in shock is 80%.2 During hypovolemia, the mother’s body considers the fetus to be nonessential and will shunt blood from the uterus, extremities and other non-essential organs to maintain core perfusion. Due to the 50% increase in blood volume during pregnancy, the mother will maintain normal vital signs until blood loss exceeds 50%.2

Placental abruption is the most common cause of fetal death in motor vehicle crashes.4 It occurs with 30%–50% of major trauma injuries.2 The rate of maternal death is low, but the rate of fetal death from placental abruption is high.6 Placental abruption is caused when shearing forces rip the placenta from the uterine walls.2 4 This, in turn, interrupts the necessary flow of oxygen and nutrients to the fetus. Typical signs of placental abruption—spontaneous rupture of membranes, vaginal bleeding and uterine tenderness—are infrequent after trauma.3

Uterine injury, either rupture or laceration, is very rare, but the outcome is nearly 100% fatal for the fetus. Uterine injury can occur from direct loading from the seat belt, or compression and loading by the steering wheel or dash if the pregnant occupant is unrestrained.4 A University of Michigan Transportation Research Institute study found that, in 48 of 69 placental abruption cases, the pregnant occupant was unrestrained.4

Like uterine injury, direct fetal injury is rare, occurring in fewer than 10% of crashes with pregnant occupants.4 Head trauma is the most common direct fetal injury. The head is the largest portion of the fetus, thus the biggest target. It is thought that head trauma results from being compressed between the maternal pelvic bones and the steering wheel or dash.4

After the 20th week of pregnancy, the mother should not rest in a supine position. The growing uterus compresses the inferior vena cava and can decrease cardiac output by as much as 30%. This compression of the inferior vena cava can cause supine hypotension syndrome.2 Uterine displacement must be maintained throughout on-scene assessment and care, transport and emergency department evaluation.6

Front-impact crashes were most common in a study of 120 automotive crashes with injuries or fatalities to pregnant occupants where the occupant was at least 20 weeks pregnant and information was available on restraint use.4

In that same study of collisions with injuries or fatalities to pregnant occupants, crash severity was classified based on vehicle crush measurements and passenger and physician estimates.4

Many factors affect maternal and fetal survival after a motor vehicle crash, but it is clear from our review of the literature that proper use of restraints is the largest survival determinant. All types of injuries occur to a greater degree to unrestrained occupants.4

The mother may be so concerned about the health of her fetus that she may not realize she is injured or appreciate the severity of her injuries.5 Reassure the mother and stay true to the patient assessment system, while keeping in mind the physiological and anatomical differences of pregnancy.

After ensuring the scene is safe, inspect the mechanism. As in any motor vehicle accident, look for clues about the vehicle’s speed, type of collision, whether it rolled over, injured occupants’ seat positions and seat belt use, airbag deployment, and whether there is damage to the dash, windshield or steering wheel. The most severe injuries are often to the front-seat passenger.5

Assessment and Treatment

Is the patient’s airway open? Is breathing adequate? Secure the airway as needed with simple or advanced airways per your scope of practice and protocol. Pregnancy in itself is not a contraindication for any airways, including intubation.

Supplemental oxygen is indicated for every pregnant trauma patient and is essential to prevent maternal and fetal hypoxia.2,6 The fetus is extremely sensitive to hypoxia. Remember that peripheral pulse oximetry is a measure of the mother’s peripheral circulation, not fetal circulation. If the mother is compensating for hypovolemia, blood is being shunted away from nonvital organs, including the uterus. Maximize delivery of oxygen to the fetus by giving high-flow oxygen to the mother.3

Check for external bleeding. The increase in blood volume and pressure on the vena cava can cause more profuse bleeding from lower-extremity lacerations.5 Significant internal bleeding can occur in the uterine wall and abdominal cavity.3

For ALS care, anticipate and begin fluid resuscitation, even if no signs of hypo-volemia are present. Increased maternal blood volume allows longer compensation, but at the expense of fetal circulation.6 Deliver IV fluids, normal saline or lactated Ringer’s through large-bore catheters at a ratio of 3:1 based on estimated blood loss.3 Administer oxygen and IV fluids until hypovolemia and hypoxia are resolved.3

For BLS care, pregnant trauma patients require aggressive IV fluid resuscitation. Call for ALS intercept as soon as possible. Administer oxygen and IV fluids until hypovolemia and hypoxia are resolved.3

As with any trauma patient, do a rapid trauma exam to identify any life-threatening wounds or musculoskeletal injuries. If there are no life threats, palpate the uterus for abnormal contours that might suggest edema or internal bleeding.5 During the focused physical, if time allows, examine the abdomen and genitals. The uterus displaces other organs and the abdomen feels tense, making it difficult to assess guarding or rigidity.5 Check for the location, type, intensity and radiation of any abdominal pain. Check for any vaginal bleeding or fluid discharge.5 Vaginal bleeding after trauma is an ominous sign of placental abruption.5 Unfortunately, physical exam findings are not reliable in predicting negative adverse fetal outcomes, due to the many anatomical and physiological changes of pregnancy.3 Is there any tightening or pain that could be contractions since the accident? Occasional uterine contractions are a common finding after blunt trauma to a pregnant woman.3 In most cases, these resolve in a few hours and are not associated with adverse fetal outcomes.3

Trauma stimulates the sympathetic nervous system. Catecholamine release causes vasoconstriction, including the utero placental blood vessels, which compromises fetal circulation.6

If spinal immobilization is indicated, prevent supine hypotension syndrome. If the length of pregnancy is at least 20 weeks, deflect the uterus off the great blood vessels of the abdomen by immobilizing the patient 15 degrees to the left by placing towels or blankets beneath the spine board.2,3 Alternatively, immobilize the patient in the left lateral position.

Pneumatic antishock garments or military antishock trousers are not indicated for pregnant hypovolemic patients; however, they may be used for stabilizing or splinting lower-extremity fractures.

Consider adding these additional questions as time allows and if the patient is awake and has stable vital signs:5, 6

  • Length of pregnancy?
  • Any complications during pregnancy?
  • Any previous pregnancies?
  • Any deliveries/miscarriages?
  • Since the accident, has she felt the fetus move?
  • Does she know her baseline vitals during pregnancy?

After treating any initial-assessment life threats and evaluating for other maternal injuries, consider a fetal assessment if gestation age is at least 24 weeks. Fetal heart tones should be audible from a normal stethoscope. Feel for movement and ask the mother if she feels the fetus moving.

All pregnant occupants of a motor vehicle collision should receive physician evaluation. Fetal death can occur even if the mother has no visible injuries.3 Transport considerations include:

  • For BLS services, the need for an ALS intercept
  • Does the receiving hospital have labor and delivery capabilities?
  • If pre-term delivery is imminent or the mother is in decompensated shock, can you transport to a hospital with a NICU?

ALS providers should check with local protocols before administering antihypotensive medications to a hypovolemic pregnant patient. Avoid any medications that will worsen peripheral vasoconstriction.5 Ephedrine causes minimal peripheral vasoconstriction.5 Dopamine in low doses may also be authorized by medical control.5 Magnesium sulfate can be used to halt pre-term labor.5

Many of us know someone who knows someone who used to ride with a paramedic who did a successful emergency c-section after the mother was deceased. If there is any chance of fetal survival, gestational age needs to be at least 24 weeks. Our advice is simple: Call medical control before considering such heroic actions. If, during your assessment, vaginal birth appears imminent, prepare OB supplies, maintain supplemental maternal oxygenation, continue fluid administration and deliver as trained.

As you make transport and resuscitation decisions, consider this information regarding successful postmortem c-section: The time interval between maternal death and delivery is strongly related to fetal survival.7 The maternal cause of death, fetus health prior to maternal death and the quality of resuscitation are also linked to survival.

Injury Prevention

An outstanding opportunity for community education and injury prevention is for EMS to educate pregnant women about proper seat belt use. Despite the high rate of adverse outcomes for unrestrained pregnant accident victims, seat belt use is low. It is the easiest and best factor to dramatically increase maternal and fetal survival from motor vehicle collisions.3

Follow these guidelines for proper seat belt use and positioning:3,4

  • Always fasten and keep seat belt fastened
  • Sit at least 10 inches from the steering wheel
  • Position lap belt below prominence of pregnant abdomen
  • Place shoulder harness off to the side of uterus, between breasts and over midline of the clavicle
  • Tilt wheel toward chest, away from abdomen
  • Do not disable airbags.

Summary

To summarize:

  • The best fetal protection is proper maternal use of seat belt restraints.
  • All pregnant occupants in a motor vehicle crash require physician evaluation.
  • Focus on maternal assessment.
  • Maternal stability is the best indicator of fetal stability.
  • Key treatments are high-flow oxygen, IV fluid loading and immobilizing in left lateral position.
  • Evaluate the fetus after maternal stabilization.

References

  1. Newton E. Trauma and pregnancy. Retrieved 11/20/2004 from www.emedicine.com/med/topic3268.htm.
  2. Chang A. Pregnancy, trauma. Retrieved 11/20/2004 from www.emedicine.com/EMERG/topic484.htm.
  3. Grossman N. Blunt trauma in pregnancy. American Family Physician 70(7):1303–1310, 2004.
  4. Klinich K, Schneider L, Moore J, Pearlman M. Injuries to Pregnant occupants in automotive crashes. Retrieved 11/20/2004 from www.nhtsa.dot.gov/esv/16/98S9P17.PDF.
  5. Pillitteri A. Maternal and Child Health Nursing, pp. 356–361. Philadelphia: Lippincott, 1999.
  6. Desjardins G. Management of the injured pregnant patient. Retrieved 11/20/2004 from www.trauma.org/resus/pregnancytrauma.html.
  7. Tintinalli JE, Ruiz E, Krome RL. Emergency Medicine: A Comprehensive Study Guide. American College of Emergency Physicians. New York: McGraw-Hill Companies, 1996.

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