In 1997, Flamm et al published a series involving 453 women attempting VBAC who had unfavorable cervices and received PGE2 for cervical ripening.16 Fifty-one percent delivered vaginally, and 6 (1.3%) experienced uterine rupture. Flamm and colleagues found no differences in perinatal or maternal morbidity between women receiving PGE2 and those who managed without it.
Several small series have described labor induction with misoprostol in the VBAC population.17-19 These studies reported uterine-rupture rates ranging from 0 to 6%. A randomized trial comparing misoprostol with oxytocin among VBAC patients was terminated prematurely because of 2 uterine ruptures among 17 women who received misoprostol.20 Consequently, misoprostol cannot be recommended for use among women with prior cesarean deliveries.
The largest single report on induction of labor comes from a Swiss database.6 In this series, there were 2,459 labor inductions, with 1,612 (65.6%) women delivering vaginally. There were 17 uterine ruptures (0.7%). Unfortunately, the authors of this series do not provide information on the means used to induce labor.
Most recently, Lydon-Rochelle and colleagues compared the uterine rupture rates among women experiencing spontaneous labors with those having their labors induced.21 The labor-induction group included women who were given prostaglandins. In the study, the risk of uterine rupture among women experiencing spontaneous labor was 0.5%, compared with 0.8% among those induced without prostaglandins, and 2.5% among those induced with prostaglandins.
VBAC: a timeline
- 1916 Origination of the aphorism: “Once a cesarean, always a cesarean.” According to Enkin et al, the phrase was a warning to avoid primary cesarean whenever possible because it always entailed a classic or T-shaped incision.1
- 1970s Research begins into the safety of vaginal birth after cesarean (VBAC). The national cesarean rate remains below 5%, while the number of VBACs starts to rise.2
- 1981 The National Institutes of Health (NIH) recommend a trial of labor for women with a previous cesarean. The rate of successful VBAC is 3%, and the overall cesarean rate is 17.9%.3
- 1984 ACOG recommends that VBAC be offered to women who have 1 or more low transverse uterine scars, provided the fetus is in a vertex presentation and there are no contraindications to vaginal delivery.3
- 1993 The Los Angeles County–University of Southern California Medical Center requires all women meeting ACOG criteria to attempt VBAC but abandons the policy in 1995 because of legal claims associated with adverse outcomes.3
- 1996 McMahon et al publish an influential study suggesting that maternal morbidity is greater with a trial of labor than with elective repeat cesarean.4 The cesarean rate peaks at 26%, then declines slightly. The VBAC rate is 28%.2
- 1999 The cesarean rate continues to rise, while the VBAC rate declines to 23%.2 ACOG modifies the criteria for VBAC to include only women with no more than 2 prior cesarean deliveries.3
REFERENCES
1. Enkin M, Keirse MJNC, Neilson J, et al, eds. A Guide to Effective Care in Pregnancy and Childbirth. Oxford, UK: Oxford University Press; 2000.
2. Caughey AB, Mann S. Vaginal birth after cesarean. eMed J. 2001;2(9).:Available at http//emedicine.com/med/topic3434.htm. Accessed June 20, 2002.
3. Harer WB, Jr. Vaginal birth after cesarean delivery: current status. JAMA. 2002;287:2627.-
4. McMahon MJ, Luther ER, Bowes WA, Jr, Olshan AF. Comparison of a trial of labor with an elective second cesarean section. N Engl J Med. 1996;335:689-695.
Risk scoring and decision models
Based on these estimates of maternal and fetal risks, a number of authors have attempted to optimize outcomes using decision analysis. They have constructed models estimating the probability of a successful TOL, as well as maternal and fetal morbidity, among women with differing clinical characteristics. The authors of 2 early models theorized that perinatal morbidity and mortality associated with uterine rupture would be offset by neonatal morbidity and mortality due to respiratory distress syndrome (RDS) after ERC.22-23 They also assumed that maternal morbidity and mortality after a TOL would be less than that after ERC. Given these assumptions, TOL was the preferred choice in both models.
A TOL may be the more cost-effective option when the probability of vaginal delivery exceeds 0.74%.
The authors of a more recent decision analysis approached the controversy differently. They calculated cost-effectiveness ratios for ERC, defining “effectiveness” as the procedure’s ability to prevent some uterine ruptures, some perinatal deaths, and some cases of long-term childhood morbidity.24 Maternal morbidity was stratified according to whether the mother experienced vaginal birth, ERC, or emergency intrapartum cesarean. In the analysis, the preferred intended mode of delivery varied, depending on the probability of successful vaginal birth based on clinical characteristics. This model suggested that a TOL may be the more cost-effective option when the probability of vaginal delivery exceeds 0.74%. Below this threshold, ERC may be more cost-effective.