Uterine Rupture

Etiology

Within pregnant women, there are two populations at risk for uterine rupture: those who have a myometrial scar from previous surgery and those with an unscarred uterus. The cause and risk factors for each group are different. 

Great attention has been paid to the large increase in the cesarean section rate in the United States over the past five decades. The cesarean section rate increased by 25% between 1970 and 2016.[5] TOLAC is one strategy to decrease the rate of cesarean births. The TOLAC has been shown to reduce maternal morbidity and mortality during the index pregnancy as well as future deliveries.[6] While a successful vaginal birth resulting from TOLAC is associated with less morbidity than a scheduled cesarean delivery, a failed TOLAC that ends in cesarean delivery is associated with more morbidity than a scheduled cesarean delivery.[5][7] Thus, the safety of TOLAC is directly tied to the probability of successful vaginal birth. Amongst the complications associated with TOLAC, uterine rupture is associated with the largest increase in maternal and neonatal morbidity.[5] Furthermore, it is estimated that the rate of uterine rupture is approximately 15-30 times higher when women undergo a TOLAC compared to a scheduled repeat cesarean delivery.[7][6]

In women who attempt a TOLAC, those with a previous midline (inverted T or J shaped or classical cesarean section) incision are at two to three times higher risk for uterine rupture than those with a previous low segment transverse incision.[6][8] Misoprostol administration is associated with an increased rate of uterine rupture.[5] The American College of Obstetricians and Gynecologists now recommends against administering misoprostol to women undergoing a TOLAC, with the exception only given to those women with a fetal demise.[5] Interestingly, a history of prior vaginal delivery significantly reduces the risk of subsequent uterine rupture.[9]

While the incidence of unscarred uterine rupture is low, the rate is increasing.[10] The rupture of an unscarred uterus causes significantly more maternal and neonatal morbidity than the rupture of a scarred uterus.[1] Most ruptures involving unscarred uteri can be traced to one of the following etiologies: (1) trauma, (2) a genetic disorder associated with uterine wall weakness, (3) a prolonged induction or augmentation of labor, or (4) overstretching of the uterine wall. 

In the United States, most major abdominal trauma that occurs during pregnancy is due to falls and motor vehicle accidents.[11] Concern for uterine rupture is one reason fetal monitoring is required after blunt abdominal trauma. Uterine rupture is also a concern during internal podalic and external cephalic versions. For this reason, some obstetricians avoid neuraxial anesthesia because they believe a uterine rupture may be missed if neuraxial anesthesia conceals rupture-associated pain. Neuraxial anesthesia for external cephalic version has been shown to improve patient comfort and improve the rate of successful version.[12][13]

The uterine wall, or myometrium, is weakened in conditions such as Ehlers-Danlos and Loeys-Dietz, which increases the risk of rupture.[14][15] A uterine rupture in a woman that has not had a previous cesarean section is now a criterion that is used to diagnose vascular Ehlers-Danlos syndrome.[16][17] 

Prolonged uterine exposure to oxytocin and other uterotonic medications increases uterine wall stress and can lead to rupture, especially in the setting of obstructed labor.[5][18] Women who experience a uterine rupture are more likely to have received oxytocin for induction or augmentation of labor compared to women without a rupture.[19]

Conditions such as gestational diabetes with macrosomia, polyhydramnios, multiple gestation pregnancy, and uterine anomalies such as fibroids can stretch the myometrium beyond its optimal range.[5][20] These conditions are associated with a higher risk of uterine rupture. There is also evidence that serial stretching of the uterine wall, such as occurs in multiparous women, may increase the risk of rupture.[1]

Epidemiology

Overall, it is estimated that one uterine rupture occurs for every 5,000 to 7,000 births.[18][21] The incidence of uterine rupture in both scarred and unscarred uteri is increasing worldwide.[10] 

Uterine rupture is more common in women with prior cesarean delivery.[3] The rate of uterine rupture is highly dependent upon the number of cesarean deliveries a woman has had and the type of uterine incision present. The rate of uterine rupture is approximately 1% for women with one previous cesarean delivery versus 3.9% for those with greater than one previous cesarean delivery.[22][23] 

The rate of uterine rupture with an unscarred uterus has been found to be approximately one rupture per 10,000 to 25,000 deliveries.[19][22] The incidence of uterine rupture in an unscarred uterus is higher in developing countries.[24] It is hypothesized that this rate is higher because techniques to manage obstructed labor, such as instrument-assisted and cesarean delivery, are less readily available.[24]

Pathophysiology

Uterine rupture refers to the complete division of all three layers of the uterus: the endometrium (inner epithelial layer), myometrium (smooth muscle layer), and perimetrium (serosal outer surface). Generally speaking, the term uterine rupture implies that a gravid uterus is involved—though ruptures have been reported in nonpregnant uteri. A uterine rupture can allow a part of the fetus, amniotic fluid, or the umbilical cord to enter the peritoneal cavity or broad ligament. A uterine rupture can cause abdominal pain, vaginal bleeding, a change in the contraction pattern, or a nonreassuring fetal heart rate tracing.

History and Physical

The presentation of a woman with a uterine rupture is highly dependent upon whether they have a labor epidural, a scared or unscarred uterus, and the location of the rupture. 

For women with a suspected uterine rupture, the initial assessment is for hemodynamic stability. Blood pressure and heart rate should be obtained to assess for hypotension and tachycardia. Common symptoms of hypotension include lightheadedness, dizziness, nausea, vomiting, and anxiety. Most of the bleeding associated with a uterine rupture is intraabdominal and cannot be detected by the patient. When vaginal bleeding occurs, it is helpful to differentiate between light spotting and significant blood-soaked linen. 

Bladder injury is not uncommon with uterine rupture.[25] Patients with a suspected uterine rupture should have their urine examined for hematuria. Pink, red, or brown urine can imply the presence of red blood cells. Blood clots can also pass through the urethra—these can be painful. 

Patients with a uterine rupture may describe acute onset abdominal pain that begins with a “ripping” sensation. Subsequent contracts are often quite painful. Chest pain may occur if blood enters the peritoneum. Blood in the peritoneum can irritate the diaphragm and cause referred to shoulder or chest pain similar to ischemic cardiac pain. A labor epidural may mask the pain associated with a uterine rupture and lead to delayed diagnosis.[26] 

The fetal heart rate provides insight into both the health of the fetus and the health of the woman—the fetal heart rate is one of the most sensitive indicators of maternal end-organ perfusion. Reduced blood flow to the fetus can present as fetal bradycardia, reduced variability, or late decelerations. Fetal bradycardia is the most common abnormality associated with uterine rupture.[3][5] No fetal heart rate tracing is pathognomonic for uterine rupture.[21] The absence of fetal heart sounds is obviously an ominous sign and requires an ultrasound to confirm absent cardiac activity. 

Palpating the abdomen to localize the area of most pain and guarding can be helpful in women with a suspected uterine rupture. A uterine rupture should cause midline pain. Most women with a uterine rupture will have a tender abdomen, even when receiving labor epidural analgesia. Palpation of the abdomen can also provide insight into whether the contraction pattern or uterine shape has changed. Uterine contraction amplitude may decrease, and contractions may stop altogether in women who experience a uterine rupture.[27][28] 

An internal examination can identify products of conception, fresh blood, or clots in the vaginal canal. In a uterine rupture, the vaginal canal is usually not full of blood—unless the tear extends into the vagina or cervix. Speculum examination may help diagnose non-pregnancy related bleeding such as a laceration or abnormal cervical growth. A vaginal exam can also identify loss of fetal station (movement of the fetal presenting part towards the abdominal cavity), which can occur with a uterine rupture if part of the fetus enters the peritoneum.

Evaluation

Due to the potential for serious maternal and neonatal morbidity, uterine rupture must be excluded in all cases of vaginal bleeding during pregnancy. The classic symptoms described for uterine rupture include acute onset abdominal pain, vaginal bleeding, a non-reassuring fetal heart rate tracing, and a change in the contraction pattern on tocodynamometry.[3][29] Unfortunately, these symptoms are often not present.[3] Radiographic and laboratory tests can be helpful in diagnosing a minor uterine rupture. Imaging is not appropriate when there is a significant rupture because of the emergent need for delivery and hemorrhage control.

The most important initial laboratory test is hemoglobin or hematocrit. If significant bleeding has occurred, coagulation tests (prothrombin time, activated partial thromboplastin time, fibrinogen, thromboelastogram) should be considered. If significant bleeding has not yet occurred, baseline hemoglobin or hematocrit can be used to monitor for ongoing blood loss. 

In a stable patient with a possible minor rupture, an ultrasound can be helpful to rule out other etiologies for vaginal bleeding, such as placenta previa, placental abruption, or spontaneous abortion. The following findings on abdominal ultrasound support the diagnosis of uterine rupture: an abnormality in the uterine wall, a hematoma next to a hysterotomy scar, free fluid in the peritoneum, anhydramnios, or fetal parts outside the uterus.[30][31] 

Ultimately, the diagnosis of uterine rupture is often confirmed when hemoperitoneum and fetal parts are identified during laparotomy.

Treatment / Management

A uterine rupture must prompt immediate action. A delay in delivery, resuscitation, or surgery increases maternal and fetal risk.[32] A uterine rupture will typically be associated with fetal bradycardia. Thus, the initial treatment step is an emergent cesarean delivery—with or without an exploratory laparotomy. General endotracheal anesthesia is typically required to facilitate quick delivery—even when a labor epidural is in place. Labor epidurals take 5 to 15 minutes to achieve a surgical block; this is typically an unacceptable delay in the setting of uterine rupture. General anesthesia has the added advantages of allowing for better management of the maternal acid-base status through adjustment of minute ventilation, stabilizing the airway, and providing neuromuscular blockade to facilitate laparotomy. Lastly, neuraxial anesthesia is contraindicated in the setting of hemodynamic instability and in patients with severe bleeding diathesis.(B2)

A uterine rupture requires simultaneous delivery and treatment of maternal hemorrhage.[22] A second large-bore intravenous line should be placed, and blood should be ordered and brought to the operating room. If large-bore intravenous access cannot be obtained, central venous access with a large bore sheath introducer should be considered. Initial resuscitation is often provided by infusing Lactated Ringer's electrolyte solution. Brisk and large volume blood loss should prompt early blood transfusion. If bleeding is not quickly controlled, an arterial line will improve the accuracy and frequency of blood pressure monitoring, lead to a shorter response to hypotension, and facilitate serial laboratory tests. 

A midline abdominal incision, as opposed to the Pfannenstiel incision, should be considered when intraperitoneal bleeding is suspected. A midline incision provides better surgical exposure for the identification of the bleeding source and may shorten the time interval between surgical incision and delivery.[33] In a smaller rupture, the uterus may be amenable to repair.[21] When there is hemodynamic instability or significant uterine injury, a hysterectomy is indicated. Approximately one in three women who experience uterine rupture require a hysterectomy.[6][34](B2)

Differential Diagnosis

The differential diagnosis for second and third trimester vaginal bleeding in the setting of acute abdominal pain includes spontaneous abortion, bloody show associated with normal labor, placenta previa, placental abruption, and uterine rupture. 

A spontaneous abortion (also referred to as an early pregnancy loss or a miscarriage) can be diagnosed by finding fetal tissue in the cervical canal either by palpation or visualization during the speculum exam within the first 20 weeks of gestation.

Bloody show refers to mucus mixed with blood that is discharged prior to the onset of labor. Bloody show may precede labor by as much as three days. The blood loss associated with bloody show is small, and patients remain hemodynamically stable.

Placenta previa refers to the placenta attaching to the uterus over the cervical opening. A placenta previa is one of the more common causes of second and third trimester bleeding.[35] The classic description of placenta previa is painless vaginal bleeding unaccompanied by uterine contractions. However, some patients with placenta previa may have crampy contraction pain. Most placenta previas can be diagnosed by ultrasound.[36] It is important not to perform a digital examination in patients with 2nd or 3rd trimester vaginal bleeding until a placenta previa has been ruled out. Digital examination of the cervix when a placenta previa is present may result in life-threatening maternal hemorrhage.[37] 

A placental abruption refers to the placenta separating from the uterus before delivery. Most placental abruptions occur around 25 weeks.[38] In an abruption, maternal blood vessels tear away from the decidua basalis, the uterine endometrium at the site of placentation, and push the placenta and uterus apart. Patients may report vaginal bleeding, acute onset abdominal pain, and continuous crampy contractions due to blood irritation.[39] Similar to a uterine rupture, placental abruption may cause non-reassuring fetal heart rate changes.[40] However, placental abruption is more likely to be associated with tetanic uterine activity than a uterine rupture.[39] Significant blood can accumulate behind a placental abruption and remain undetectable by ultrasound examination. Ultrasonography has poor sensitivity for diagnosing a placental abruption.[41] If blood loss is significant, an abruption can be life-threatening for both the woman and the neonate.

Uterine rupture occurs rarely but must be ruled out in all cases of 2 and 3 trimester vaginal bleeding. The biggest risk factor for a uterine rupture is TOLAC. Most uterine ruptures occur during labor. A uterine rupture should be considered in all women undergoing a TOLAC who present with any of the following: hypotension, a sudden change in contraction pattern, fetal bradycardia, sudden abdominal pain, hematuria, loss of fetal station, or vaginal bleeding.

Prognosis

With quick surgical intervention and resuscitation, most women survive a uterine rupture. The maternal mortality rate associated with the rupture of an unscarred uterus is higher (10%) than the mortality rate associated with the rupture of a scarred uterus (0.1%).[42][43] The neonatal mortality rate after uterine rupture is 6% to 25%.[3][7][44] 

The risk of recurrent rupture after the uterine repair is not well described.[45] This is because the incidence of rupture is low, and many women with a significant uterine rupture require a hysterectomy. In a few small case series conducted outside the United States, the incidence of repeat rupture was 33% to 100%.[34][46] There is low-level evidence that the repeat rupture rate may be higher when the initial rupture occurs in the uterine fundus.[46] Due to the maternal and fetal risk of repeat rupture, most obstetricians recommend repeat cesarean delivery between 36 and 37 weeks—before labor is allowed to begin.[5][45]

Complications

The incidence of serious fetal and maternal morbidity depends upon the location and magnitude of the rupture as well as the speed of surgical intervention. Lateral ruptures are associated with worse outcomes than midline ruptures—perhaps because of increased vascularity of the lateral uterine wall. A longer time to surgical intervention is associated with more maternal blood loss, a higher risk of coagulopathy, and longer fetal exposure to hypoxia.[32]

Rupture of unscarred uteri is associated with more blood loss, a higher incidence of hysterectomy, and a higher rate of composite maternal morbidity (death, hysterectomy, blood transfusion, or urologic injury) than rupture of scarred uteri.[1] The incidence of composite fetal neurologic injury (intraventricular hemorrhage, seizure, death, or brain ischemia) is also higher for ruptures involving an unscarred uteri, compared to scarred uteri.[1] The rate of fetal mortality is 10% for unscarred uteri and 2% for scarred uteri.[1]