Obstetric Anesthesia Identifying Risk Factors for Uterine Rupture

U terine rupture, a catastrophic and feared complication, occurs occasionally in women attempting a vaginal birth after a previous cesarean delivery (VBAC). An inherent risk of uterine rupture is also associated with a uterine scar. Because of concerns about the safety of VBAC, the number of women attempting this has declined 67% since 1996, and was tried by only 9.2% of women in 2004. Although the risk of uterine rupture is low (0.16%) following VBAC, a repeat cesarean delivery (CD) carries risks of bleeding, infection, and damage to surrounding structures. One study of women who had a history of a prior CD found that more women undergoing an elective CD died compared with those attempting a trial of labor. Most uterine ruptures are associated with VBAC, but a nulliparous uterus can also rupture. Spontaneous uterine rupture is rare, estimated to occur in 1 in 8000 to 1 in 15,000 deliveries. Uterine rupture has been attributed to uterine anomalies secondary to a history of diethylstilbestrol exposure, bicornuate uteri, Ehlers-Danlos syndrome, agents used to induce and augment labor, and abnormal placentation. Uterine rupture, estimated at 31% of all uterine ruptures, can also occur in primigravid patients who have had previous uterine surgery, including myomectomy, even laparoscopic myomectomy, the most common procedure to remove pedunculated and subserosal myomas. Induction and augmentation of labor in these women should be managed similar to procedures in women undergoing VBAC. Intrapartum signs associated with uterine rupture in women who have had a previous cesarean section include presence of abdominal pain between contractions, vaginal bleeding, loss of fetal station, and nonreassuring fetal heart rate patterns. By the time these signs are present and recognized, major maternal and neonatal morbidity may have already developed. Intrapartum predictors include changes in the fetal heart rate, especially bradycardia and late decelerations. Other clinical signs in one studywere abdominal pain continuing between contractions, vaginal bleeding, loss of fetal station, and a palpable uterine defect. Antepartum predictors include previous spontaneous vaginal delivery, previous successful VBAC, maternal age, maternal obesity, number of previous CDs, type of closure of the previous uterine incision, gestational age at delivery, and the interval between pregnancies. For a woman considering VBAC, the type of uterine incision (low transverse, low vertical, classical, or unknown) is critical because risk of rupture differs depending on the location of this incision. Rates for low transverse and low vertical incisions are 0.7% and 2.0%, respectively, and the rates for a classical incision range from 4% to 9%. A singleor double-layered uterine closure may influence VBAC success and uterine rupture rates. Women who have had a previous successful vaginal delivery have a higher chance of successful VBAC and a decreased risk of uterine rupture. The effect of the interpregnancy interval is uncertain, with studies showing conflicting data. However, a CD within the previous 2 years may increase the risk of rupture in a woman undergoing VBAC. Vaginal birth after a previous cesarean delivery has success and a lower rate of uterine rupture in preterm women. One study found no uterine rupture cases in women undergoing a trial of labor at less than 32weeks gestation. Olderwomen are at an increased risk of adverse outcomes during VBAC, including an increased risk of uterine rupture. Obese women need counseling regarding the optimal mode of delivery after a previous CD. Induction and augmentation of labor with misoprostol in women with a previous cesarean section has been associated with uterine hyperstimulation and increased rates of uterine rupture. Administration of oxytocin is probably safe in these patients although some studies have found an increased risk of uterine rupture with oxytocin induction of labor after a CD. Another factor to consider in women electing VBAC is that the risk for maternal morbidity is increased if the VBAC is not successful. The timing of elective repeat CD is important and the CD should be performed at 39 completed weeks of gestation. Perinatal morbidity is another consideration. Hypoxic ischemic encephalopathy is more common in women who undergo a trial of labor compared with those who have a repeat CD. The failed trial of labor is also associated with major neonatal morbidities, including sepsis, respiratory distress syndrome, pneumonia, acidosis, intraventricular hemorrhage, subgaleal bleeding, and trauma. Currently, no methods are available to accurately predict uterine rupture. Those women wishing to have a trial of labor must be selected based on antepartum criteria, including appropriate counseling. A high index of suspicion for uterine rupture must be part of the process when managing a woman with a history of CD.