The American College of Obstetricians and Gynecologists (ACOG) recently issued clinical management guidelines for vaginal birth after cesarean delivery (VBAC) in various situations. The complete guideline, ACOG Practice Bulletin no. 54, appeared in the July 2004 issue of Obstetrics and Gynecology.
According to the report, the cesarean delivery rate in the United States increased from 5 percent to nearly 25 percent between 1970 and 1988. The authors attribute this increase to pressure on physicians to not perform vaginal breech deliveries and mid-pelvic forceps deliveries, and an increasing reliance on continuous electronic monitoring of fetal heart rate and uterine contraction patterns. Several large series found that a trial of labor after a previous cesarean delivery was relatively safe, prompting organizations such as the National Institutes of Health and the ACOG to endorse VBAC as a way to reduce the number of cesarean deliveries in the United States. Between 1989 and 1996, the cesarean delivery rate decreased as the VBAC rate increased. However, reports of uterine rupture and other complications during trials of labor after previous cesarean deliveries caused this trend to reverse.
No randomized trials have compared maternal or neonatal outcomes for repeat cesarean delivery and VBAC. Rather, VBAC recommendations have been based on data from large clinical studies suggesting that the benefits of VBAC outweigh the risks in most women with a previous low-transverse cesarean delivery. Most of these trials have been performed in university or tertiary-level centers with in-house obstetric and anesthesia coverage. ACOG notes that only a few studies have documented the relative safety of VBAC in smaller community hospitals or facilities where resources may be more limited. The report adds that women who fail a trial of labor are at risk for several maternal complications, including uterine rupture, the need for transfusion, hysterectomy, endometritis, and perinatal morbidity and mortality.
Clinical Considerations and Recommendations
According to the report, the evidence suggests that most patients who have had a low-transverse uterine incision from a previous cesarean delivery and who have no contra-indications for vaginal birth are candidates for a trial of labor. Criteria for selecting candidates for VBAC include the following: (1) one previous low-transverse cesarean delivery; (2) clinically adequate pelvis; (3) no other uterine scars or previous rupture; (4) a physician immediately available throughout active labor who is capable of monitoring labor and performing an emergency cesarean delivery; and (5) the availability of anesthesia and personnel for emergency cesarean delivery.
The report also discusses other specific obstetric circumstances where a trial of labor may be offered. According to the report, for women who have had two previous low-transverse cesarean deliveries, only those with a previous vaginal delivery should be considered candidates for a spontaneous trial of labor. They state that 60 to 90 percent of women attempting a trial of labor who give birth to infants with macrosomia are successful, and the rate of uterine rupture appears to be increased only in women who have not had a previous vaginal delivery. Awaiting spontaneous labor beyond 40 weeks of gestation decreases the likelihood of successful VBAC but does not increase the risk of uterine rupture. According to one case series and four retrospective studies, women who have had a previous low-vertical uterine incision were just as likely to have successful VBAC as women who have had a previous low-transverse uterine incision. Two trials showed no significant difference between rates of successful VBAC and uterine rupture between women with twin or singleton gestations.
SUCCESS RATES FOR TRIALS OF LABOR
Most published series of women attempting a trial of labor after a previous cesarean delivery demonstrate that 60 to 80 percent have successful vaginal births. ACOG reports that for an individual patient, there is no completely reliable way to predict the success of a trial of labor. Success rates are similar for women whose first cesarean delivery was performed for a nonrecurring indication and for women who have not undergone a previous cesarean delivery. Although most women who have undergone a cesarean delivery because of dystocia can have a successful VBAC, the percentage may be lower (50 to 80 percent) than for those with nonrecurring indications (75 to 80 percent). Women who have given birth vaginally at least once are nine to 28 times more likely to have a successful trial of labor than women who have not given birth vaginally. The likelihood of failure of a trial of labor is reduced by 30 to 90 percent if the most recent delivery was a successful VBAC. The likelihood of successful VBAC is impacted negatively by labor augmentation and induction, maternal obesity, gestational age beyond 40 weeks, interdelivery interval of less than 19 months, and birth weight greater than 4,000 g (8 lb, 11 oz).
RISKS AND BENEFITS ASSOCIATED WITH VBAC
Repeat cesarean delivery and VBAC both have risks. Successful VBAC generally is associated with shorter maternal hospitalizations, fewer infections, less blood loss and fewer transfusions, and fewer thromboembolic events than cesarean delivery. However, a failed trial of labor may be associated with major maternal complications, such as hysterectomy, uterine rupture, operative injury, increased maternal infection, need for transfusion, and neonatal morbidity. Multiple cesarean deliveries are associated with an increased risk of placenta previa and accreta.
With VBAC, the incidence of maternal death is extremely low. The incidence of perinatal death is less than 1 percent, and is more likely to occur during a trial of labor than an elective repeat cesarean delivery.
Uterine rupture during a trial of labor after a previous cesarean delivery is a life-threatening complication directly associated with attempted VBAC. The patient’s obstetric history influences the risk of uterine rupture. A previous vaginal birth significantly reduces the risk of uterine rupture. Also, the longer the length of time between deliveries, the lower the risk of rupture. Women who attempt VBAC who have interdelivery intervals of less than 24 months have a two- to three-fold increased risk of uterine rupture compared with women whose interdelivery interval is more than 24 months.
INDUCTION OR AUGMENTATION OF LABOR
A successful VBAC is more likely to result from spontaneous labor than labor induction or augmentation. The report states that evidence shows that cervical ripening with prostaglandin preparations increases the likelihood of uterine rupture. Misoprostol also has been associated with a high rate of uterine rupture in women with a previous cesarean delivery. The report recommends not using prostaglandins for induction of labor in most women with a previous cesarean delivery.
The decision to attempt a trial of labor in the midtrimester in women with a previous cesarean delivery should be based on the patient’s individual circumstances, including the number of previous cesarean deliveries, placentation, gestational age, and the woman’s desire to preserve reproductive function.
Summary of Recommendations
The following recommendations are based on good and consistent scientific evidence (Strength of Recommendation Taxonomy [SORT] = A; see page 1201 for an explanation of SORT):
• Most women with one previous cesarean delivery with a low-transverse incision are candidates for VBAC and should be counseled about VBAC and offered a trial of labor.
• Epidural anesthesia may be used for VBAC.
The following recommendations are based on limited or inconsistent scientific evidence (SORT = B):
• Women with a vertical incision within the lower uterine segment that does not extend into the fundus are candidates for VBAC.
• The use of prostaglandins for cervical ripening or induction of labor in most women with a previous cesarean delivery should be discouraged.
The following recommendations are based primarily on consensus and expert opinion (SORT = C):
• Because uterine rupture may be catastrophic, VBAC should be attempted in institutions equipped to respond to emergencies with physicians immediately available to provide emergency care.
• After thorough counseling that weighs the individual benefits and risks of VBAC, the ultimate decision to attempt this procedure or undergo a repeat cesarean delivery should be made by the patient and her physician. This discussion should be documented in the medical record.
• Vaginal birth after a previous cesarean delivery is contraindicated in women with a previous classical uterine incision or extensive transfundal uterine surgery.