Examining the Evidence
Q How likely is uterine rupture in VBAC attempts?
<huc>A</huc> The incidence was less than 1% in this study. Uterine rupture occurred in 9.8 of 1,000 attempts at vaginal birth after cesarean delivery (VBAC). Previous vaginal delivery decreased the risk of uterine rupture by 60%. Although use of prostaglandins did not increase the risk of rupture, sequential use of a prostaglandin and oxytocin did.
The popularity of VBAC is waning in the United States, due mainly to concerns about complications after uterine rupture. The most recent national data show that the VBAC rate, which was 28.3% in 1996, declined to a mere 9.2% in 2004.1 In this context, Macones and colleagues undertook their multicenter case-control trial to determine the incidence of and risk factors for uterine rupture in a variety of hospital settings.
Study involved both community and tertiary-care hospitals
This is the largest trial to date to analyze VBAC success rates in university/tertiary care centers and community hospitals (with or without residency programs) to verify whether the typically quoted uterine rupture rate of less than 1% can be generalized to most settings.2 Macones et al used International Classification of Diseases, 9th revision (ICD-9) codes to perform this retrospective cohort review, identifying 13,706 patients who attempted VBAC in a 5-year period. Within this cohort, after reviewing all the charts, they performed a nested case-control comparison of uterine ruptures and nonruptures in a 5 to 1 ratio.
Women most likely to succeed had prior vaginal delivery
Recent studies have also sought to identify women less likely to experience uterine rupture with VBAC.3-5 In the Macones study, among historical risk factors for uterine rupture, only prior vaginal delivery affected rupture rates, decreasing the incidence by 60% (odds ratio [OR] 0.40; 95% confidence interval [CI] 0.20–0.81).
Hendler and Bujold6 also found that a history of vaginal delivery lowered the VBAC uterine rupture rate—to 0.5%, versus 1.4% in women without that history (P=.02). But they cautioned that this finding may be incidental. Other studies that explored effects of previous vaginal delivery focused on VBAC success rather than uterine rupture. The finding that a previous vaginal delivery increases the likelihood of VBAC success has remained consistent.6-10
How this study differs from others
Macones et al found that neither labor induction with prostaglandins, induction with oxytocin, nor augmentation with oxytocin affected rupture rates. However, sequential use of prostaglandins and oxytocin did increase these rates (OR 4.54; 95% CI 1.66–12.42; P=.003). These findings contrast those of a cohort study by Lydon-Rochelle et al,11 who used ICD-9 codes without chart review to estimate the incidence of uterine rupture in the Washington State Birth Events Database. Using elective repeat cesarean as their reference group, Lydon-Rochelle et al found a 15-fold increase in rupture rates when labor was induced with prostaglandins (relative risk 15.6; 95% CI 8.1–30.0).
Don’t switch to prostaglandins just yet. In response primarily to the Lydon-Rochelle study, the American College of Obstetricians and Gynecologists published a Committee Opinion12 in April 2002, discouraging the use of prostaglandins to induce labor in women attempting VBAC. In the current study by Macones and colleagues, the authors pointed out that prostaglandin E2 (and not misoprostol or prostaglandin E1) was the only type of prostaglandin used in all centers evaluated. Thus, although the study by Macones et al is well designed, it is retrospective and should not encourage the use of prostaglandins for VBAC until the question has been answered prospectively.
Encourage VBAC in women who have delivered vaginally
Overall, the study by Macones et al adds important information to the literature. The uterine rupture rate (<1%) seen with VBAC attempts is generalizable to the community setting, and VBAC attempts are appropriate provided a physician capable of performing emergent cesarean is immediately available, as well as anesthesia and OR personnel.2
In women who have delivered vaginally, VBAC should be encouraged. However, the use of prostaglandins to induce labor in these cases warrants further investigation.
The author reports no financial relationships relevant to this article.
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