- Although the risk of uterine rupture and fetal complications may be slightly increased with a trial of labor (TOL), the overall incidence of these complications is low.
- In a recent meta-analysis involving 47,682 women, a TOL produced more favorable maternal outcomes than elective repeat cesarean (ERC). Women choosing TOL also were much less likely to undergo hysterectomy than those selecting ERC.
- Many investigators remain reluctant to recommend induction of labor in the setting of vaginal birth after cesarean section (VBAC), fearing an increased risk of uterine rupture when oxytocic agents are used.
- Between 374 and 809 women would need to undergo ERC to prevent 1 uterine rupture, and between 693 and 3,332 women would need to undergo ERC to prevent 1 perinatal death attributable to a TOL.
Despite numerous studies detailing the safety and efficacy of attempted vaginal birth after cesarean (VBAC), the strategy remains controversial. Many obstetricians are retreating from the assumption that this mode of delivery is safer than elective repeat cesarean (ERC) for most women with 1 or 2 prior cesarean sections. This shift in attitude springs in part from a decreased societal tolerance of risk and in part from a misinterpretation of current data.
Here, I review a large body of literature supporting the contention that a trial of labor (TOL) yields a more favorable maternal risk profile than ERC. Although the risk of uterine rupture and fetal complications may be slightly increased with a TOL, the overall incidence of these complications is reassuringly low.
Absolute risks and benefits
Research into the relative safety of a TOL after cesarean was conducted throughout the 1970s and 1980s. In 1989, Meehan and Magani published data from 15 years of experience at the University College Hospital in Galway, Ireland.1 This series included 1,350 trials of labor, with an 81.26% vaginal delivery rate. Among the women who labored, the incidence of true uterine rupture (which the authors defined as “complete uterine scar disruption, requiring repair at emergency cesarean section or laparotomy”) was 0.44%. In comparison, the incidence of true rupture among the 1,084 women who opted for ERC was 0.37%. There were 4 perinatal deaths attributable to uterine ruptures; 3 occurred in the TOL group, and 1 occurred in the ERC group.
Other evidence from large databases includes a meta-analysis by Rosen and Dickinson, which pooled data from studies carried out in the United States between 1982 and 1989.2 Among the 29 studies included in the analysis, the rate of successful vaginal delivery ranged from 54% to 89%.
A later meta-analysis by Rosen et al compared morbidity and mortality for TOL and ERC.3 In 5,463 trials of labor, there were 22 true uterine ruptures (4/1,000), with 3 perinatal deaths (5/10,000) attributable to these ruptures. There was one maternal death in each group, yielding maternal mortality rates of 2.8 in 10,000 for women choosing a TOL and 2.4 in 10,000 for women undergoing ERC. Maternal febrile morbidity was greatest among women having failed a TOL, intermediate among women undergoing ERC, and lowest among women having successful TOLs. This analysis did not compare maternal morbidity according to intended mode of delivery.
Subsequently, several large series compared TOL with ERC. One from California prospectively compared these delivery options among women receiving obstetrical care within the Kaiser Permanente managed-care organization.4 This cohort study included 5,022 women who attempted vaginal birth, and 2,207 women who underwent ERC. Among women attempting vaginal birth, 75% were successful, with a rate of uterine rupture of 0.8%. There were no perinatal deaths due to rupture, and women attempting vaginal birth required significantly fewer transfusions and had significantly less postpartum fevers than those undergoing ERC. There were fewer hysterectomies among women in the TOL group than the ERC group, though the difference was not statistically significant.
Febrile morbidity was less common among women having a TOL than an ERC.
In another series, Miller et al reported a prospective evaluation of TOL and ERC among 17,322 women with at least 1 previous cesarean who delivered at the University of Southern California Women’s Hospital or at Los Angeles County Hospital.5 Of these women, 12,707 had trials of labor, with 82% delivering vaginally. There were 95 uterine ruptures (0.7%), but the rate of related perinatal death was only 2 in 10,000.
More recently, Rageth and colleagues evaluated 29,046 deliveries after previous cesarean in a pooled Swiss database of 457,825 deliveries.6 Of these patients, 17,613 underwent a TOL, with a success rate of 73.7%. There were 70 uterine ruptures among the women attempting vaginal birth (0.4%) and 22 ruptures among those undergoing ERC (0.2%). Perinatal death was more common among those undergoing a TOL, but the absolute risk of perinatal death was low (2/1,000 for TOL compared with 1/1,000 for ERC when infants with congenital anomalies or extreme prematurity were excluded). Hysterectomy, febrile morbidity, and thromboembolic complications all were significantly less common among women having a TOL than those choosing elective repeat cesarean.