Trauma in pregnancy

Journal of Family Practice, Dec, 1993 by Francis L. Agnoli, Mark E. Deutchman

Trauma is the leading cause of nonobstetric maternal morbidity and mortality in this country. Maternal survival does not guarantee fetal survival, even in cases of apparently minor trauma. The injured pregnant patient presents unique diagnostic and therapeutic challenges. Physicians who make obstetrics or emergency medicine part of their practice must be aware of these unique problems. Prevention of traumatic injury should remain the focus of office practice.

Trauma is the leading nonobstetric cause of morbidity and mortality in pregnancy, and in some studies it accounts for twice the number of deaths caused by obstetric complications.[1,2] The incidence of trauma in pregnancy is estimated at 6% to 7%, with blunt trauma being most common.[1-6] Blunt trauma is usually due to motor vehicle accidents; falls and assaults are less frequent causes.[1-7] The incidence of minor trauma, especially falls, increases as pregnancy progresses. This increase is most likely due to fainting, pelvic joint laxity and pain, and the awkwardness of movement caused by a protuberant abdomen.[5,8]

When a pregnant patient suffers trauma, maternal survival does not guarantee fetal survival.[2,5,6] Fetal death rates in pregnant trauma victims exceed maternal death rates three- to ninefold.[4] Many of these fetal deaths occur in cases of insignificant maternal injury.[2,4-6,8,9] For this reason, physicians who practice obstetrics or emergency medicine must develop a rational approach to the evaluation of traumatized pregnant patients that will optimize both maternal and fetal survival and incur the least costs from medical testing and hospital confinement.

Changes in Pregnancy

As pregnancy progresses, the uterus enlarges from a pelvic to an intra-abdominal organ, becoming more susceptible to injury. As the uterus expands into the abdominal cavity, other organs are displaced, changing the spectrum of injuries seen in abdominal penetrating trauma. Stretching of the abdominal wall decreases the signs of peritoneal irritation in pregnant women.[2,8,10,11]

Changes in maternal physiology during pregnancy alter the patient's hemodynamic status and therefore may mask the signs and symptoms of hypovolemic shock.[2-4,6,10-12] For example, plasma volume, cardiac output, and heart rate are all increased in pregnant patients. Blood pressure can be decreased by as much as 15 mm Hg by midtrimester. Laboratory changes associated with pregnancy are outlined in Table 1.

By the end of pregnancy, plasma volume has increased 40% to 50% over prepregnancy values. This relative hypervolemia allows for the loss of 30% to 35% of blood volume without the development of hypotension.[3,4,6,11] Cardiac output has increased by 20% to 30%.[2,3,10,11] Maternal blood flow is often maintained at the expense of uteroplacental flow, placing the fetus at risk for hypoxic injury or death. This shunting of maternal blood away from the uterus is secondary to the greater adrenergic response and lack of autoregulation found in the uterine vasculature.[2-4,6,10,11] It is critical to remember that simply placing even a normal pregnant patient in the supine position can cause severe hypotension resulting from compression of the inferior vena cava and subsequent decreased venous return.[10,11]

[TABULAR DATA OMITTED]

Spectrum of Injury

The pregnant trauma patient is susceptible to a unique set of problems. Placental abruption is second only to maternal death as the most common cause of fetal death, complicating 1% to 5% of minor and 6% to 50% of major injuries.[3,4,8-10] Placental position does not appear to affect the incidence of abruption.[2] Vaginal bleeding is usually absent.[8]

Uterine rupture is very rare, present in only 0.6% of pregnant trauma victims.[2,10] Although maternal mortality is low (around 10% and due to associated severe injuries), fetal mortality approaches 100%.[2,10]

Direct fetal injury resulting from trauma is also rare, especially in the first trimester when the uterus is shielded by the pelvis. Most direct fetal injuries involve the cranium and its contents, and are usually associated with maternal pelvic fractures in the second and third trimesters.[2,7,8,10,11]

Fetomaternal hemorrhage, or loss of blood from the fetal to the maternal circulation, is four to five times more common in the traumatized patient than in uninjured controls. This complication is associated with anterior placental location, the presence of uterine tenderness, and motor vehicle accidents rather than other types of blunt trauma. Severity of maternal injury does not appear to correlate with the presence of fetomaternal hemorrhage, but large hemorrhages ([greater than] 5 mL) are seen only in patients with physical evidence of trauma.[2,9,10]

If mild, fetomaternal hemorrhage results only in fetal and subsequent neonatal anemia. If more severe, signs of hypovolemia may be evident on fetal heart rate monitoring, such as fetal tachycardia, a sinusoidal pattern, or late decelerations. In severe cases, fetal death due to exsanguination may occur. Maternal isoimmunization may occur if there is blood group or Rh incompatibility between the mother and the fetus.[2,9,10,13,14]