Trauma in pregnancy ranges from mild (a single fall from standing height or hitting the abdomen on an object such as an open desk drawer) to major (penetrating or high force blunt motor vehicle crash). Although infrequently encountered in the clinical setting, emergency medicine physicians, trauma surgeons and OBGYN's should aware of and prepared to manage a variety of complications associated with trauma in pregnancy. With sufficient knowledge of normal maternal physiology and potential pregnancy-related injury patterns, the physician facing a pregnant trauma victim will be better equipped to manage them, thus resulting in reduced morbidity and mortality.[1][2]

Etiology of trauma in pregnancy may be multifactorial.  The physics of the growing abdomen results in an imbalance which may lead to falls from standing or down stairs.  Further, the clinician must maintain a high suspicion for non-accidental causes, either self-inflicted or other.  The normal physiology of the pregnant mother complicates evaluation and management of trauma in pregnancy. The gravid uterus is particularly suspectible to penetrating and blunt trauma to the abdomen. Domestic violence increases during pregnancy, placing the mother and the fetus at high risk for injury.  [3][4]

Six to 7% of pregnancies involve trauma and regardless of mechanism, can be life threatening for both the maternal and fetal patient.  [5][6]

Anatomic and Physiologic Changes in Pregnancy. To be able to recognize abnormal vital signs and injuries in a pregnant patient, normal anatomic and physiologic changes in pregnancy must be understood. Multiple organ systems undergo changes during pregnancy, the major, pertinent systems are discussed herein.[7][8]

Abdominal Changes. The tone of the lower esophageal and gastric motility is reduced in pregnancy.  This leads to reflux and retained food contents in the stomach, respectively.  Because of these factors, there is an increased risk of aspiration, especially during intubation. The peritoneum stretches markedly and by the third trimester becomes much less sensitive to peritoneal irritation.  Even in patients with traumatic hemoperitoneum, they may not exhibit abdominal tenderness on examination due to the peritoneal stretching and insensitivity (AHC media, trauma reports.  Current Concepts in the Management of the Pregnant Trauma Patient.  Author: Dennis Hanlon, MD). The uterus eventually becomes the largest intraabdominal organ.  Its walls become thin and susceptible to injury.  Blood flow increases from a non-pregnant state of 60 ml/min to an impressive 600 ml/min at term.  As in the typical blunt trauma patient, the spleen remains the most commonly injured organ.

Hematologic Changes. Both the plasma volume and the red cell mass increase throughout pregnancy.  Plasma volume doubles by the end of the third trimester, however, in much higher proportion than the red blood cell mass increase.  This results in dilutional anemia of pregnancy.  The normal hemoglobin is 10-14 grams per deciliter by the term.  The liver becomes hypermetabolic, increasing production of coagulation factors and fibrinogen.  With this production, the patient is now more at risk for deep vein thrombosis and disseminated intravascular coagulation (DIC).  DIC panels must be interpreted with caution.  Because it is expected to have elevated fibrinogen levels at term, a normal fibrinogen level may indicate DIC.

Pulmonary Changes. Respiratory rate (RR) x tidal volume (TV) = Minute ventilation (MV).  RR does not change during pregnancy.  Counterintuitively, TV is increased by 40%, leading to a 40% increase in MV.  This leads to a lowered partial pressure of carbon dioxide (PCO) of 30 mmHg (normal values are in the range 35-45 mmHg), resulting in a chronically compensated respiratory alkalosis. This must be taken into account when evaluating a blood gas. The diaphragm is elevated by approximately 2-4 cm at term.  This is essential to know when performing a tube thoracostomy.  Chest tubes should be placed in the same mid-axillary line, however, 2 cm higher to avoid potential puncture into the liver or spleen.  Lastly, the Mallampati score, an airway assessment score used prior to intubation, is an estimated distance from the base of the tongue to the roof of the mouth.  Mallampati classification ranges from 1-4: 1 denoting all inner oral cavity structures visible, to 4, wherein only the hard palate is visible. The Mallampati score increases throughout pregnancy, leading to a greater percentage of levels 3 and 4. Given all of these pulmonary changes, a pregnant trauma has potential to result in a difficult airway scenario.

Cardiovascular Changes. Pregnancy-related cardiovascular changes require careful interpretation of the vital signs in the trauma patient.  Pulse in the 3rd trimester elevates 15-20 beats per minute.  The blood pressure goes down by 15-20 mmHg, however, returns to normal during the 3rd trimester.  Any sign of hypotension should be evaluated immediately given this return to the normal level.  It should not be attributed to the pregnant state as this is an interpretation of exclusion in the setting of trauma.  Finally, as noted previously, the plasma volume rises by 50%, thus leading to a potentially delayed recognition of shock.  By the time the maternal blood pressure falls, the patient may have already sustained a 30% blood loss.

Pregnancy Related Injuries. As with any trauma, certain injury patterns are likely.  There are injuries unique to pregnancy that must be considered in addition to these.

Premature Labor. Premature labor is defined as the presence of uterine contractions occurring at less than 36 weeks’ gestation (premature) accompanied by cervical changes (labor).  Although trauma patients may feel pain similar to real labor contractions, these pains may not represent contractions.  Toconometry is indicated to determine if the contractions are real.  The most common cause is placental abruption (see below).  If contractions are present, the diagnosis of placental abruption must be considered and investigated, as well as uterine rupture and other hemorrhage. If present, correction of hypoxia and hypovolemia should occur as these are common causes of premature labor.

Placental Abruption. Placental abruption is the leading cause of fetal death not related to maternal death.  It occurs in 1-5% of minor trauma.  It is important to note that the classic triad of vaginal bleeding, abdominal pain, and uterine irritability may not be present.  The edges of the placenta may encase the bleeding internally, in addition to the peritoneum being markedly insensitive given the massive stretching near term. Ultrasound may be helpful in the diagnosis but is not sensitive.  If the ultrasound does not reveal abruption, the diagnosis is not ruled out.  Regardless, toconometry is required for minimum 4 hours and may be extended by the obstetrical team for a multitude of reasons.

Amniotic Fluid Embolus. Uncommon and catastrophic, the pathophysiology of amniotic fluid embolus is currently poorly understood.  The patient may present much like a massive pulmonary thrombotic embolus.  There is no specific treatment for this entity, with exception of supportive care, intubation, vasopressors, and transfusion.

Uterine Rupture. Although a rare complication of trauma (0.06%), fetal mortality approaches 100% when present.  It most often occurs in the 3rd trimester.  Because of the high amount of force required to cause uterine rupture, it is commonly associated with pelvic fractures and bladder injuries.  The classic presentation is dramatic; abdominal pain, distention (due to the unfolding of the fetus), palpable fetal parts, and shock.  However, given the peritoneum's insensitivity in the 3rd trimester, there may be no pain present. High index of suspicion accompanied by prompt recognition is critical.  Treatment is exploratory laparotomy, delivery of fetus and supportive care.