Trial of Labor and Vaginal Birth After Cesarean Delivery
David H. Chestnut MD
Chapter Outline
PRIMARY CESAREAN DELIVERY: CHOICE OF UTERINE INCISION
In 1916, Edward Cragin1 stated, “Once a cesarean, always a cesarean.” This edict has had a profound effect on obstetric practice in the United States. The cesarean delivery rate increased from 5.5% of all deliveries in 1970 to 24.7% in 1988 (Figure 19-1). Much of the increase in the cesarean delivery rate resulted from performance of repeat cesarean deliveries. In contemporary practice, elective repeat cesarean deliveries account for one third of all cesarean deliveries. Cesarean delivery is the most frequently performed major surgery in the United States.
For many years most U.S. physicians ignored Cragin’s subsequent statement, “Many exceptions occur.”1 In 1981 the National Institute of Child Health and Human Development Conference on Childbirth concluded that vaginal birth after cesarean (VBAC) is an appropriate option for many women.2 In 1991, Rosen et al.3 modified Cragin’s original dictum as follows: “Once a cesarean, a trial of labor should precede a second cesarean except in the most unusual circumstances.” In 1988 and again in 1994, the American College of Obstetricians and Gynecologists (ACOG)4 concluded: “The concept of routine repeat cesarean birth should be replaced by a specific decision process between the patient and the physician for a subsequent mode of delivery.… In the absence of a contraindication, a woman with one previous cesarean delivery with a lower uterine segment incision should be counseled and encouraged to undergo a trial of labor in her current pregnancy.”
The VBAC rate increased from 2% in 1970 to 28% in 1995. This change in practice helped reduce the overall cesarean delivery rate from 24.7% in 1988 to 20.7% in 1996 (see Figure 19-1). Subsequently the safety of a trial of labor after cesarean (TOLAC) underwent further scrutiny and criticism, and the VBAC rate sharply declined.5 The VBAC rate in the United States dropped from 28% in 1995 to 9% in 2004. Meanwhile, in 2009, the overall cesarean delivery rate rose to 32.9%, the highest rate ever recorded in this country.6
Primary Cesarean Delivery: Choice of Uterine Incision
Obstetric practice in 1916 hardly resembled obstetric practice today. In 1916, only 1% to 2% of all infants were delivered by cesarean delivery. Most cesarean deliveries were performed in patients with a contracted bony pelvis, and obstetricians uniformly performed a classic uterine incision (i.e., a long vertical incision in the upper portion of the uterus) (Figure 19-2). A patient with a classic uterine incision is at high risk for catastrophic uterine rupture during a subsequent pregnancy. Such uterine rupture may occur before or during labor, and it often results in maternal and perinatal morbidity or mortality.
FIGURE 19-2 Uterine incisions for cesarean delivery. A, Low-transverse incision. The bladder is retracted downward, and the incision is made in the lower uterine segment, curving gently upward. If the lower segment is poorly developed, the incision also can curve sharply upward at each end to avoid extending into the ascending branches of the uterine arteries. B, Low-vertical incision. The incision is made vertically in the lower uterine segment after reflection of the bladder, with avoidance of extension into the bladder below. If more room is needed, the incision can be extended upward into the upper uterine segment. C, Classic incision. The incision is entirely within the upper uterine segment and can be at the level shown or in the fundus. D, J-shaped incision. If more room is needed when an initial transverse incision has been made, either end of the incision can be extended upward into the upper uterine segment and parallel to the ascending branch of the uterine artery. E, T-shaped incision. More room can be obtained in a transverse incision by an upward midline extension into the upper uterine segment. (Modified from Landon MB. Cesarean delivery. In Gabbe SG, Niebyl JR, Simpson JL, editors. Obstetrics: Normal and Problem Pregnancies. 5th edition. Philadelphia, Churchill Livingstone Elsevier, 2007:493.)
In 1922, De Lee and Cornell7 advocated the performance of a vertical incision in the lower uterine segment. Unfortunately, low-vertical incisions rarely are confined to the lower uterine segment. Such incisions often extend to the body of the uterus, which does not heal as well as the lower uterine segment. Kerr8 later advocated the performance of a low-transverse uterine incision (see Figure 19-2). A low-transverse uterine incision results in less blood loss and is easier to repair than a classic uterine incision.9 Further, a low-transverse uterine incision is more likely to heal satisfactorily and to maintain its integrity during a subsequent pregnancy. Thus, obstetricians prefer to make a low-transverse uterine incision during most cesarean deliveries.
Obstetricians reserve the low-vertical incision for patients whose lower uterine segment does not have enough width to allow safe delivery. Preterm parturients may have a narrow lower uterine segment. In these patients, delivery through a transverse uterine incision may cause an extension of the incision into the vessels of the broad ligament. For example, a patient with preterm labor at 26 weeks’ gestation may undergo cesarean delivery because of a breech presentation, and the obstetrician may perform a low-vertical incision to facilitate an atraumatic delivery of the fetal head.
Obstetricians rarely perform a classic uterine incision in modern obstetric practice. An obstetrician may perform a classic uterine incision when the need for extensive intrauterine manipulation of the fetus (e.g., delivery of a fetus with a transverse lie) is anticipated. Some obstetricians prefer a classic uterine incision in patients with an anterior placenta previa. In such cases, the performance of a classic incision allows the obstetrician to avoid cutting through the placenta, which might result in significant hemorrhage.
Maternal and Neonatal Outcomes
Multiple studies have demonstrated that TOLAC results in a successful VBAC in 60% to 80% of women in whom a low-transverse uterine incision was made for a previous cesarean delivery.10–13 A 2010 National Institute of Health (NIH) consensus development panel14 concluded that although the TOLAC rate has declined dramatically in recent years, the VBAC rate after TOLAC has remained constant at approximately 74%. However, the panel acknowledged that many published studies were observational and did not address issues of selection bias. The panel also noted that a history of vaginal delivery, either before or after a prior cesarean delivery, is consistently associated with an increased likelihood of successful VBAC.14
Maternal Outcomes
Flamm et al.10 performed a prospective multicenter study of TOLAC. Of the 7229 patients, 5022 (70%) underwent TOLAC and 2207 underwent elective repeat cesarean delivery. Some 3746 (75%) of the women who opted for TOLAC delivered vaginally. The incidence of uterine rupture was 0.8%. The incidence of postpartum transfusion, the incidence of postpartum fever, and the duration of hospitalization were significantly lower in the TOLAC group than in the elective repeat cesarean group. Likewise, in a 1991 meta-analysis of 31 studies, Rosen et al.3 noted that maternal febrile morbidity was significantly lower among women who attempted VBAC than among those who underwent elective repeat cesarean delivery.
In contrast, McMahon et al.15 performed a population-based longitudinal study of 6138 women in Nova Scotia who had previously undergone cesarean delivery and who delivered a single live infant between 1986 and 1992. Some 3249 women attempted VBAC, and 2889 women chose a repeat cesarean delivery. There was no difference between the two groups in the incidence of “minor complications” (e.g., puerperal fever, transfusion, wound infection). However, “major complications” (e.g., hysterectomy, uterine rupture, operative injury) were nearly twice as common among women who attempted VBAC than among women who underwent elective repeat cesarean delivery.
Landon et al.11 subsequently conducted a prospective 4-year observational study of all parturients with a singleton gestation and a prior cesarean delivery at 19 academic medical centers. Among the 17,898 women who attempted VBAC, 13,139 (73.4%) delivered vaginally. Symptomatic uterine rupture occurred in 124 (0.7%) women who underwent a trial of labor. The rate of endometritis was higher in women who underwent a trial of labor than in women who had an elective repeat cesarean delivery (2.9% versus 1.8%), as was the rate of blood transfusion (1.7% versus 1.0%).15
In a 2004 systematic review of published studies of attempted VBAC, Guise et al.16 observed no significant difference in the incidence of maternal death or hysterectomy between women who attempted a trial of labor and those who underwent repeat cesarean delivery. Uterine rupture was more common in the women who attempted a trial of labor, but the rates of asymptomatic uterine dehiscence did not differ.
Wen et al.17 performed a retrospective cohort comparison of outcomes after TOLAC or elective repeat cesarean delivery in 308,755 Canadian women with a history of previous cesarean delivery. These investigators observed that the rates of uterine rupture (0.65%), transfusion (0.19%), and hysterectomy (0.10%) were significantly higher in the TOLAC group. However, the maternal in-hospital death rate was significantly lower in the TOLAC group (1.6 per 100,000) than in the elective cesarean delivery group (5.6 per 100,000). Similarly, Guise et al.18 observed a lower maternal mortality rate in women who underwent TOLAC than in women who underwent elective repeat cesarean delivery (0.004% versus 0.013%, respectively).
Cahill et al.19 performed a multicenter cohort study in which they concluded that among TOLAC candidates who had a prior vaginal delivery, those who attempted VBAC had a lower risk for overall major maternal morbidities, as well as maternal fever and transfusion, than women who chose repeat cesarean delivery. These investigators concluded that women who have had a prior vaginal delivery have “less composite maternal morbidity if they attempt VBAC compared with [those] undergoing an elective repeat cesarean delivery.” Further, they concluded that a trial of labor is “a safer overall option for women who have had a prior vaginal birth.”19
Rossi and D’Addario12 performed a meta-analysis of studies published in 2000-2007 that compared maternal morbidity in women who underwent TOLAC versus women who underwent elective repeat cesarean delivery. Successful VBAC occurred in 17,905 (73%) of 24,349 women who underwent TOLAC. Overall maternal morbidity did not differ between women who underwent TOLAC and women who underwent elective repeat cesarean delivery. Likewise, the incidence of blood transfusion and hysterectomy did not differ between the two groups. The incidence of uterine rupture was higher in the TOLAC group (1.3% versus 0.4%). Further, maternal morbidity, uterine rupture, blood transfusion, and hysterectomy were more common in women who had a failed TOLAC.
The 2010 NIH consensus development panel14 noted that the overall benefits of TOLAC “are directly related to having a [successful] VBAC as these women typically have the lowest morbidity.” Likewise, the panel noted that the harms of TOLAC “are associated with an unsuccessful trial of labor resulting in cesarean delivery because these deliveries have the highest morbidity.” However, the panel concluded that women who undergo TOLAC, regardless of the ultimate mode of delivery, are at decreased risk for maternal mortality compared with women who undergo elective repeat cesarean delivery. The panel also cited low-grade evidence of a shorter hospitalization overall for women attempting TOLAC compared with women undergoing elective repeat cesarean delivery.
Neonatal Outcomes
Lydon-Rochelle et al.20 conducted a population-based, retrospective cohort analysis of obstetric outcomes for all 20,095 nulliparous women who gave birth to a live singleton infant by cesarean delivery in civilian hospitals in Washington between 1987 and 1996 and who subsequently delivered a second singleton child during the same period. These investigators observed that spontaneous labor was associated with a tripling of the risk for uterine rupture (i.e., a uterine rupture rate of 5.2 per 1000 women who had spontaneous onset of labor versus 1.6 per 1000 women who underwent elective repeat cesarean delivery without labor). Further, the incidence of infant death was more than 10 times higher among the 91 women who experienced uterine rupture than among the 20,004 who did not (i.e., a 5.5% incidence of infant death versus a 0.5% incidence, respectively).20
In the study performed by McMahon et al.15 there was no difference between the two groups in perinatal mortality or morbidity. However, two perinatal deaths occurred after uterine rupture in the TOLAC group. Landon et al.11 observed that hypoxic-ischemic encephalopathy occurred in no infants whose mothers underwent elective repeat cesarean delivery and in 12 infants delivered at term whose mothers underwent a trial of labor (P < .001).
The 2010 NIH consensus development panel14 concluded that the perinatal mortality rate (death between 20 weeks’ gestation and 28 days of life) is increased with TOLAC when compared with elective repeat cesarean delivery (i.e., 130 deaths per 100,000 infants compared with 50 deaths per 100,000 infants, respectively). Likewise, the panel concluded that the neonatal mortality rate (death in the first 28 days of life) is also increased with TOLAC when compared with elective repeat cesarean delivery (110 deaths per 100,000 infants versus 50 deaths per 100,000 infants, respectively).14
On the other hand, successful VBAC avoids the neonatal risks of elective cesarean delivery. Inappropriate assessment of gestational age or fetal maturity occasionally leads to the delivery of a preterm infant. Elective cesarean delivery results in some cases of iatrogenic neonatal respiratory sequelae, including respiratory distress syndrome and transient tachypnea of the newborn. Kamath et al.21 observed that newborns born after elective repeat cesarean delivery had significantly higher rates of respiratory morbidity and neonatal intensive care unit admission—and a longer length of hospital stay—than infants whose mothers attempted VBAC. However, the 2010 NIH consensus development panel14 concluded that there is insufficient evidence to determine whether substantial differences in respiratory outcomes occur in infants born via elective repeat cesarean delivery compared with infants born after TOLAC.
Eligibility and Selection Criteria
Most studies suggest a high likelihood of success with TOLAC, even in women in whom the indication for previous cesarean delivery was dystocia or failure to progress in labor. Rosen and Dickinson22 performed a meta-analysis of 29 studies of attempted VBAC. Among women whose previous cesarean deliveries were performed for dystocia or cephalopelvic disproportion, the average rate of successful VBAC was 67%. Later studies have concluded that a history of previous vaginal delivery (including previous VBAC) is the greatest predictor for successful VBAC.23
The highest risk for maternal morbidity and mortality is associated with unsuccessful TOLAC.14 The ACOG13 concluded that women with at least a 60% to 70% chance of successful VBAC have equal or less maternal morbidity when they undergo TOLAC than women who undergo elective repeat cesarean delivery. Conversely, the ACOG13 noted that women who have a lower than 60% probability of successful VBAC have a greater likelihood of morbidity than women who undergo elective repeat cesarean delivery. Thus, the ability to identify women with a high likelihood of successful VBAC would improve the safety of TOLAC. Investigators have attempted to develop reliable scoring systems for predicting the success or failure of TOLAC, with limited success. Grobman et al.24 developed a nomogram specifically for women undergoing TOLAC at term gestation with one previous low-transverse cesarean delivery, a singleton gestation, and a vertex fetal presentation. The nomogram incorporates six variables that may be ascertained at the first prenatal visit; those variables include maternal age, body mass index, ethnicity, prior vaginal delivery, prior VBAC, and a recurring indication for cesarean delivery. This model was validated in a subsequent study.25
The ACOG13 concluded that the “preponderance of evidence suggests that most women with one previous cesarean delivery with a low-transverse incision are candidates for and should be counseled about VBAC and offered TOLAC.” A history of dystocia, a need for induction of labor, and maternal obesity are associated with a lower likelihood of successful VBAC.24,26–28
History of More Than One Cesarean Delivery
Studies that have assessed outcomes of TOLAC in women with a history of more than one cesarean delivery have not demonstrated consistent conclusions. One large multicenter study found no increased risk for uterine rupture (0.9% versus 0.7%) in women with more than one previous cesarean delivery, when compared with women with only one previous cesarean delivery.29 A second large study observed that the risk for uterine rupture increased from 0.9% to 1.8% during TOLAC in women with two previous cesarean deliveries.30 Both studies observed that TOLAC was associated with some increase in maternal morbidity in women with more than one previous cesarean delivery, although the absolute magnitude of the difference in morbidity was relatively small.29,30 The ACOG13 concluded that it is reasonable to consider TOLAC for women with two previous low-transverse cesarean deliveries. Data regarding the risk of TOLAC in women with more than two previous cesarean deliveries are limited.13
Previous Low-Vertical Incision
Some obstetricians allow a trial of labor after a previous low-vertical uterine incision, provided that there is documentation that the uterine incision was confined to the lower uterine segment. (Low-vertical uterine incisions often extend above the lower uterine segment, especially when performed in preterm patients.) Naef et al.31 retrospectively reviewed outcomes for 174 women who attempted VBAC after a previous low-vertical cesarean delivery; 144 (83%) women delivered vaginally. Uterine rupture occurred in 2 (1.1%) of the patients. These investigators concluded that “the likelihood of successful outcome and the incidence of complications are comparable to those of published experience with a trial of labor after a previous low-segment transverse incision.”31 Adair et al.32 made similar observations. The ACOG13 concluded that there is no consistent evidence of an increased risk for uterine rupture in women with a previous low-vertical uterine incision, and that obstetricians and patients may choose to undergo TOLAC in the presence of a documented prior low-vertical uterine incision.
Twin Gestation
Some obstetricians believe that uterine overdistention, which occurs with twin gestation, increases the risk for uterine rupture in patients with a history of previous cesarean delivery. Early reports suggested otherwise, but these studies were limited by the small number of patients.33,34 Cahill et al.35 performed a retrospective cohort study of 25,005 obstetric patients with at least one previous cesarean delivery, which included 535 patients with a twin pregnancy. The investigators observed that women with a twin gestation were less likely to attempt VBAC but were no more likely to have a failed VBAC or to experience major morbidity than women with a singleton gestation.
Likewise, a report from the Maternal-Fetal Medicine Unit Cesarean Registry36 included outcome measures for 186 women with a twin gestation who attempted VBAC. Some 120 (64.5%) women delivered vaginally. Women who attempted a trial of labor with twin gestation had no higher risk for transfusion, endometritis, intensive care unit admission, or uterine rupture than women who underwent elective repeat cesarean delivery. The investigators concluded that a trial of labor in women with a twin gestation after previous cesarean delivery does not appear to be associated with a higher risk for maternal morbidity.36
Ford et al.37 subsequently examined outcomes for 6555 women with a twin gestation who delivered between 1993 and 2002. Among 1850 women who underwent a trial of labor, 836 (45.2%) delivered vaginally. The rate of uterine rupture was higher in the trial-of-labor group than in the elective cesarean delivery group (0.9% versus 0.1%), but the rate of wound complications was lower in the trial-of-labor group (0.6% versus 1.3%).
The ACOG13 concluded that “women with one previous cesarean delivery with a low-transverse [uterine] incision, who are otherwise appropriate candidates for twin vaginal delivery, may be considered candidates for TOLAC.”
Unknown Uterine Scar
For some patients, there is no documentation of the type of uterine incision performed during a previous cesarean delivery. Some obstetricians require documentation of the type of previous uterine incision before they allow a patient to attempt VBAC. At least two studies have concluded that a trial of labor does not significantly increase maternal or perinatal mortality in patients with an unknown uterine scar.38,39 Perhaps this conclusion is true because most patients with an unknown uterine scar had a low-transverse uterine incision at previous cesarean delivery. Ultrasonography may help the obstetrician confirm the presence of a low-transverse uterine scar in the pregnant woman with an unknown uterine scar.40 The ACOG13
