Most women who undertake a trial of labor after a previous cesarean delivery will achieve a successful vaginal birth, but those who fail are at higher risk of maternal morbidity than those who choose elective repeat cesarean.1 Many researchers have tried to find predictive factors of successful vaginal birth after cesarean (VBAC),2,3 the indication of the previous cesarean being one of these factors. When the indication for the previous cesarean is failure to progress secondary to cephalopelvic disproportion, the rate of successful VBAC is lower than when the indication is a nonrecurrent cause.4,5 It has been proposed by Hoskins and Gomez that a previous cesarean for dystocia in the second stage of labor is associated with a very high rate of failed trial of labor for the subsequent pregnancy.6 Contrary to this study, three studies with small numbers of patients showed a good success rate.7–9 An increased incidence of operative vaginal delivery has also been reported in these patients.10 The goal of our study was to evaluate the rate of successful trial of labor and the rate of operative vaginal delivery in patients with a previous cesarean for dystocia in the second stage of labor.
MATERIALS AND METHODS
This is an observational cohort study including all women who had a trial of labor after a previous low transverse cesarean in our institution between April 1990 and April 2000. Three databases were used to ensure that no cases were overlooked. Previous operative report, medical, and nurse's files were reviewed. Data were collected for the following variables: 1) maternal age; 2) gestational age; 3) parity; 4) previous vaginal birth; 5) indication for the previous cesarean; 6) maximal cervical dilatation at the previous cesarean; 7) birth weight at the previous cesarean and at the subsequent delivery; 8) augmentation of labor with oxytocin; 9) induction of labor; 10) use of epidural; and 11) use of vacuum or forceps.
We divided patients into three groups according to the indication for previous cesarean. Group 1 was composed of those who had a previous cesarean for dystocia in the second stage of labor; group 2 included those who had a cesarean for dystocia in the first stage of labor; and group 3 for those who had a cesarean for any other (nonrecurrent) indication, which served as a control group. The rate of spontaneous vaginal delivery, operative vaginal delivery (vacuum or forceps), and cesarean was calculated for each group. Differences between groups were assessed through proportion comparisons using Pearson's χ2 test and comparisons of means using one-way analysis of variance adjusted for inequality of variance when Brown-Forsythe homogeneity of variances test was significant.11 When a statistical difference between groups was found, post hoc tests were performed to test the differences against the control group; when variances were considered equal, we used Dunnett's rule, otherwise we used Bonferroni's rule. All tests were performed with an overall significance level of 5%, that is, P < .05 was considered statistically significant. Statistical analysis was performed using SAS release 6.12-TS060 (SAS Institute Inc., Cary, NC).
The total number of deliveries from April 1990 to April 2000 was 40,528. Of these, 4132 (10.2%) patients underwent at least one previous cesarean, and trial of labor took place in 2035 (49.2%). Of these patients, 2002 (98%) were included in our study; the remaining 33 were excluded because of incomplete data. Based on the indication of the previous cesarean, patients were divided in three groups. Group 1 included 214 patients (10.7%), group 2 included 654 patients (32.7%), and group 3 included the 1134 remaining patients (56.6%).
Table 1 compares the patients' characteristics. There were small differences between groups for maternal age and gestational age. Birth weight at the previous and subsequent pregnancy were higher in patients with a previous history of dystocia (groups 1 and 2) compared with that in the control group. Groups 1 and 2 also had a higher rate of primiparous patients and a lower rate of patients with a previous vaginal delivery compared with the control group.
Characteristics of labor and delivery are displayed in Table 2. The rate of labor induction was not different in the three groups. Group 2 patients (previous cesarean for dystocia in first stage of labor) were more likely to need augmentation of labor with oxytocin and to use epidural analgesia. The highest rate of vaginal delivery was found in group 3 with 82.5% (95% confidence interval [CI] 80.3, 84.7), followed by group 1 with 75.2% (95% CI 69.5, 81.0), and then group 2 with 65.6% (95% CI 62.0, 69.2). To eliminate the effect of having had one or more previous vaginal delivery, rates of successful VBAC were recalculated according to the parity. The rate of operative vaginal delivery (forceps or vacuum) was comparable between groups. Rate of uterine rupture was comparable between groups. There was no maternal or fetal death. The number of neonates with an Apgar score less than 7 at 5 minutes was 8 of 214 (3.7%) in group 1, 22 of 654 (3.4%) in group 2, and 28 of 1132 (2.5%) in the control group (P = .398).
Indications for the repeat cesarean were analyzed for the three groups (Table 3). We found that patients in group 1 were more likely to have a repeat cesarean for dystocia in the second stage, and those in group 2 had increased odds of having repeat cesarean for dystocia in the first stage. From 476 cesareans, 133 (27.9%) were performed for a dystocia with a cervical dilatation less than 5 cm. Finally, the rate of uterine rupture was not statistically different between groups.
In this study, of 214 patients who undertook a trial of labor after a previous cesarean for dystocia in the second stage, 161 (75%) achieved vaginal delivery with no increased risk of operative vaginal delivery. These results are quite different from those of the Hoskins and Gomez6 study, which reported a rate of successful VBAC of 13% in 245 patients who had a previous cesarean for the same reason. In contrast, our study compares well with four other studies with a smaller number of patients that reported a VBAC success rate ranging from 65% to 80% in patients with previous dystocia in the second stage of labor.7–10 All the studies, including ours, have a potential selection bias, because trial of labor is not attempted in all of the patients having had a previous cesarean. Patient preference and physicians' opinions are important determinants in patient selection for a trial of labor. The population of the Hoskins and Gomez study was comparable in terms of birth weight to our studied population, but labor augmentation with oxytocin and epidural were used less frequently. Rates of induction of labor were not reported. In the Hoskins and Gomez study, 62% of repeat cesareans after a trial of labor were performed with a diagnosis of cephalopelvic disproportion at a cervical dilatation of less than 5 cm, compared with 28% in our population. One would expect that patients who achieved full cervical dilatation at the previous delivery would again reach full cervical dilatation at the next delivery. In our series, 186 (87%) out of 214 patients in group 1 achieved full cervical dilatation. It is possible that such differences in practice patterns could influence the rate of successful VBAC.
Furthermore, our rate of instrumental vaginal delivery of 15% was much lower than the rate of 48% reported by Jongen et al.10 The main indication for the instrumental delivery was not mentioned in this study. In our series, most of the cesareans in group 1 were performed for dystocia in the second stage. In this situation, the experience and the preference of the obstetrician to perform an instrumental delivery or a cesarean will obviously influence the mode of delivery. This could be one reason why the rates of successful VBAC and instrumental delivery were higher in the Jongen study.
In conclusion, patients who have had a previous cesarean for dystocia in the second stage of labor should not be discouraged from attempting VBAC. The majority of these patients will achieve full cervical dilatation and a successful VBAC.
1. McMahon MJ, Luther ER, BowesWAJr, Olshan AF. Comparison of trial of labor with an elective second Cesarean section. N Engl J Med 1996;335:689–95.
2. Troyer LS, Parisi VM. Obstetric parameters affecting success in a trial of labor: Designation of a scoring system. Am J Obstet Gynecol 1992;167:1099–114.
3. Pickhardt MG, Martin JN Jr, Meydrech EF, Blake PG, Martin RW, Perry KG Jr, et al. Vaginal birth after cesarean delivery: Are they useful and valid predictors of success or failure? Am J Obstet Gynecol 1992;166:1811–9.
4. Miller DA, Diaz PG, Paul RH. Vaginal birth after cesarean: A 10-year experience. Obstet Gynecol 1994;84:255–8.
5. Rosen MG, Dickinson JC. Vaginal birth after cesarean: A meta-analysis of indicators for success. Obstet Gynecol 1990;76:865–9.
6. Hoskins IA, Gomez JL. Correlation between maximum cervical dilatation at cesarean delivery and subsequent vaginal birth after Cesarean delivery. Obstet Gynecol 1997;89:591–3.
7. Ollendorff D, Goldberg J, Minogue J, Socol M. Vaginal birth after cesarean section for arrest of labor: Is success determined by maximum cervical dilatation during the prior labor? Am J Obstet Gynecol 1988;159:636–9.
8. Impey L, O'Herlihy C. First delivery after cesarean delivery for strictly defined cephalopelvic disproportion. Obstet Gynecol 1998;92(5):799–803.
9. Duff P, Southmayd K, Read J. Outcome of trial of labor in patients with a single previous low transverse cesarean section for dystocia. Obstet Gynecol 1988;71:380–4.
10. Jongen VHWM, Halfwerk MGC, Brouwer WK. Vaginal delivery after previous caesarean section for failure of second stage of labour. Br J Obstet Gynaecol 1998;105:1079–81.
11. Snedecor GW, Cochran WG. Statistical methods, 6th ed. Ames, Iowa. The Iowa State University Press, 1967.