Bujold, Emmanuel MD; Blackwell, Sean C. MD; Gauthier, Robert J. MD
The decision between a trial of labor and an elective repeat cesarean delivery can be a dilemma for both the patient and health care provider. The patient’s previous delivery experience,1 the increased maternal morbidity associated with a failed trial of labor,2 and the risk of uterine rupture with possible severe neonatal morbidity3 are factors to be considered. A recent decrease in the national rate of vaginal birth after cesarean4 delivery may be a reflection of patients’ concern regarding these issues. Identification of factors associated with successful vaginal birth after cesarean delivery as well as uterine rupture might improve counseling of patients with a previous cesarean delivery. Recent studies have suggested that the use of prostaglandins for cervical ripening and/or labor induction in vaginal birth after cesarean delivery could be associated with an increased risk of uterine rupture.5,6 However, there is a paucity of information about the risk of uterine rupture associated with other methods of labor induction. The purpose of this study was to evaluate the risk of uterine rupture associated with a mechanical method of cervical ripening, the transcervical Foley catheter.
MATERIALS AND METHODS
This was an observational cohort study including all women who had a trial of labor after a previous low transverse cesarean delivery after 24 weeks’ gestation in our institution between January 1988 and December 2002. The institutional review board of Ste-Justine Hospital approved the study. Patients with multiple gestations, fetuses with lethal congenital anomalies, or stillborn fetuses were excluded. In an effort to ensure that all patients were accurately identified, three separate sources were used: our perinatal database, medical records, and the labor and delivery log book. Our perinatal database, a research-quality database, was started in 1988. Previous studies have been reported from this database.7,8 Two observers independently reviewed all previous operative reports, medical, and nursing records.
Data were collected for the following variables: maternal age, gestational age, parity, previous vaginal birth, previous vaginal birth after cesarean delivery, interval between the previous cesarean and the actual delivery, indication for the previous cesarean delivery, type of closure of the previous low transverse uterine incision, date of delivery, birth weight, augmentation of labor with oxytocin, use of epidural anesthesia, induction of labor, modified Bishop score before induction of labor, cervical ripening, and complete uterine rupture and scar dehiscence noted at the time of cesarean delivery. Modified Bishop score was defined according to Lange et al9; a maximum score of 12 was possible. The modified Bishop score consisted of cervical dilatation (maximum 6 points), effacement (maximum 3 points), and station (maximum 3 points). Uterine rupture was defined as a defect that involved the entire thickness of the uterine wall, including the overlying peritoneum, with extrusion of intrauterine contents into the peritoneal cavity.10 Dehiscence was defined as an opening of the previous scar, with intact overlying visceral peritoneum.10
In our center, labor induction in patients with a previous cesarean delivery and a favorable cervix (defined by a modified Bishop score of 6 or more or a cervical dilatation of 2 cm or more) was done by amniotomy followed with oxytocin infusion (1 mIU/min increased by 1 to 2 mIU/min every 20 to 30 minutes) when needed. When the fetal station was considered too high to safely perform amniotomy, oxytocin infusion was initiated before artificial amniotomy. For patients with an unfavorable cervix, transcervical extraamniotic Foley catheter (Foley #18, with 50 mL of sterile water in the balloon) was the method of choice used for cervical ripening before labor induction. Patients were asked to arrive the evening before the induction, and the Foley catheter was placed into the cervix. The next morning (approximately 12 hours later), labor induction was started with amniotomy, and oxytocin was added as needed. Patients with premature rupture of membranes without spontaneous labor underwent labor induction using intravenous oxytocin, regardless of the cervical status.
We divided patients in three groups: those with spontaneous labor (control group); those with labor induction by means of amniotomy with or without oxytocin, including patients undergoing induction of labor because of premature rupture of membranes; and those with an induction of labor using transcervical Foley catheter for cervical ripening. Patients who underwent an induction of labor using prostaglandins were excluded. Patients in the amniotomy with or without oxytocin group included patients with a favorable cervix who underwent an amniotomy for labor induction, followed by intravenous oxytocin if necessary; patients with a favorable cervix who underwent labor induction using oxytocin, followed by spontaneous or artificial amniotomy; and patients with spontaneous rupture of membranes without regular contractions who underwent an induction of labor using intravenous oxytocin.
The rates of vaginal delivery and uterine rupture were calculated for each group. Differences between groups were assessed through proportion comparisons using the Pearson χ2 test or the Fisher exact test when appropriate, with a Bonferroni-corrected Fisher exact test for pairwise comparisons. After a review of the literature, a logistic regression analysis was performed to adjust for potential confounding variables, including the following: maternal age 30 years or more,11 year of delivery, maternal insulin-requiring diabetes, previous cesarean delivery for labor dystocia, more than one cesarean delivery, single-layer closure of the previous lower transverse uterine segment incision,7 interdelivery interval of 24 months or less,8 unfavorable cervical status before induction (defined as a modified Bishop score of 4 or less),9 epidural anesthesia, previous vaginal delivery, and birth weight 4000 g or more. Before entry in the logistic regression model, each variable was tested for its relationship with uterine rupture and successful vaginal birth after cesarean delivery. Variables associated with uterine rupture or successful vaginal birth after cesarean delivery with P < .20 were included in the appropriate logistic regression analysis.
Comparisons of means were performed by one-way analysis of variance and Student-Newman-Keuls post hoc test for pairwise comparisons. The assumption of homogeneity of variance was tested by the Levene test. Comparisons of medians were performed by the Mann-Whitney U test. Statistical analysis was performed by SPSS 10.0 (SPSS Inc., Chicago, IL). P < .05 was considered significant.
Between 1988 and 2002, a total of 2479 patients with a previous low-transverse cesarean delivery met the inclusion criteria. Of these, 1807 patients (72.9%) had spontaneous labor and 672 (27.1%) had labor induction, which was divided into two categories: 417 (16.8%) who had labor induction by means of amniotomy with or without oxytocin and 255 (10.3%) who had induction of labor with previous cervical ripening using a transcervical Foley catheter. Patients who received prostaglandins were excluded. Prostaglandins used were prostaglandin E2 gel in eight patients and prostaglandin E2 vaginal insert in six patients. One (7.1%) uterine rupture and one incidental scar dehiscence were noted in those patients.
Comparison among the three groups is presented in Table 1. Compared with the control group, patients who underwent a labor induction by means of amniotomy with or without oxytocin had a greater gestational age and were more likely to have a previous vaginal delivery. Patients with a Foley catheter also had a greater gestational age but they were less likely to have a previous vaginal delivery. Indications for induction of labor are reported in Table 2. Patients with amniotomy with or without oxytocin were more likely to have an induction for premature rupture of membranes, whereas patients in the Foley group were more likely to have an induction for a hypertensive disorder or a gestational age greater than 41 weeks. Of note, the modified Bishop score before labor induction was greater in the amniotomy with or without oxytocin group (median 6, range 0–11) when compared with the Foley group (median 2, range 0–8) (P < .001).
In Table 3, intrapartum outcomes are reported. We found that patients who had a labor induction were more likely to receive oxytocin and to have an epidural anesthesia. When compared with patients with spontaneous labor, patients with transcervical Foley catheter had a lower rate of successful vaginal birth after cesarean delivery (78.0% versus 55.7%, P < .001), but no difference was found between patients with spontaneous labor and patients who had amniotomy with or without oxytocin (78.0% versus 77.9%). This difference found in the transcervical Foley group might be explained by a significant increased rate of cesarean delivery for dystocia in the first stage of labor (30.2% versus 10.5%, P < .001) in patients with induction of labor using a Foley catheter. After adjusting for confounding variables, including year of delivery, maternal insulin-requiring diabetes, previous cesarean delivery for labor dystocia, single-layer closure of the previous lower transverse uterine segment incision, a modified Bishop score of 4 or less, epidural anesthesia, a previous vaginal delivery, and birth weight 4000 g or more, the odds ratio (OR) for successful vaginal birth after cesarean delivery was 1.19 (95% confidence interval [CI] 0.84, 1.69) in the amniotomy with or without oxytocin group and 0.68 (95% CI 0.41, 1.15) in the Foley catheter group, when compared with patients with spontaneous labor. However, an unfavorable cervix status before labor induction (defined by a modified Bishop score of 4 or less) was associated with a statistically significant lower rate of successful vaginal birth after cesarean with an OR of 0.53 (95% CI 0.34, 0.84).
The rate of complete uterine rupture was not statistically different among the three groups (Figure 1). After adjusting for confounding variables, including year of delivery, single-layer closure of the previous lower transverse uterine segment incision, interdelivery interval 24 months or less, a modified Bishop score of 4 or less, epidural anesthesia, and a previous vaginal delivery, the OR for uterine rupture was 0.47 (95% CI 0.06, 3.59) for patients with labor induction using a transcervical Foley catheter, when compared with patients with spontaneous labor. Finally, there was no difference in the rate of asymptomatic scar dehiscence at the time of cesarean delivery among the three groups (25 of 397, 6.3%, versus 5 of 92, 5.4%, versus 3 of 113, 2.7%; P = .32).
A power analysis was performed to determine the number of patients necessary to find a statistically significant difference in the rate of uterine rupture between the two methods of induction. Assuming a rate of uterine rupture of 1.6% in patients undergoing an induction of labor with a transcervical Foley catheter compared with a rate of 1.2% in patients undergoing an induction of labor with amniotomy with or without oxytocin, a sample size of more than 12,000 patients would be necessary in each group (α = .05 and β = .20).
Of the 2479 patients who underwent a trial of labor after a previous cesarean delivery, 255 (11%) had labor induced by transcervical Foley catheter. There were no significant differences in the risk of uterine rupture when compared with the other groups. There was also no difference in the rate of reported scar disruption at the time of cesarean delivery in patients who had a failed trial of labor. These results are consistent with the findings of two previous studies involving transcervical Foley in patients who had vaginal birth after cesarean delivery. Ravasia et al6 reported only 1 uterine rupture (0.8%) in 129 patients with a previous cesarean delivery who had a transcervical Foley catheter and 2 uterine ruptures (0.7%) in 274 patients with labor induction not requiring cervical ripening. Ben-Aroya et al12 reported no cases of uterine rupture in 161 patients who underwent cervical ripening using transcervical Foley catheter. Finally, Khotaba et al13 studied 38 patients with previous cesarean delivery who had cervical ripening before labor by another mechanical method, a double-balloon device, without uterine rupture. Our power analysis showed that more than 24,000 patients would be needed to find a significant difference in the rate of symptomatic uterine rupture between induction of labor using transcervical Foley catheter compared with amniotomy with or without oxytocin.
We found that patients who underwent an induction of labor with previous cervical ripening using a Foley catheter were less likely to achieve a vaginal birth after cesarean delivery (56% overall, and 49% in women without a previous vaginal delivery). Ben-Aroya et al12 reported a rate of successful vaginal birth after cesarean delivery of 51% in 161 primiparous patients with a previous cesarean delivery who had a transcervical Foley catheter compared with 65% in their control group of patients with spontaneous labor. However, in the current study, after adjusting for confounding variables, the use of Foley catheter for cervical ripening was not a significant factor associated with failed trial of labor. Instead, we found that a modified Bishop score of 4 or less was associated with an increase of failed trial of labor. This finding is consistent with McNally and Turner,14 who demonstrated that cervical effacement before induction of labor was associated with successful vaginal birth after cesarean delivery. Flamm and Geiger15 also reported a significant correlation between cervical status at the time of admission and successful vaginal birth after cesarean delivery.
On the basis of our data, we believe that labor induction using transcervical Foley catheter is not associated with an increased risk of uterine rupture when compared with spontaneous labor. Thus, an unfavorable cervix should not solely defer a patient with previous cesarean delivery against a trial of labor; however, the rate of successful vaginal birth after cesarean delivery can be lower, especially in patients with no previous vaginal delivery.
Health care providers should consider the benefits and the risks of mechanical versus pharmacologic methods of cervical ripening. In two randomized controlled trials involving patients without uterine scar undergoing induction of labor, Sciscione et al16,17 found the transcervical Foley catheter had several benefits when compared with prostaglandin E2 gel or intravaginal misoprostol, including a shorter induction time and less contractile abnormalities. In our population, only 14 patients received prostaglandins for cervical ripening, and thus, few conclusions could be drawn. In the largest series of patients who had vaginal birth after cesarean delivery in whom prostaglandin E2 was used, Flamm et al18 did not find an increased risk of uterine rupture (1.3% versus 0.7%, P = .27). It is noteworthy that the majority of the patients included in that study had some degree of cervical dilatation (median 1 cm) and effacement (median 10–50%) at the time of initial prostaglandin E2 gel placement. On the other hand, Ravasia et al6 and Lydon-Rochelle et al5 found an increased risk of uterine rupture with the use of prostaglandins. However, neither of these two studies reported the cervical status before the use of prostaglandins nor adjusted their results for it. Finally, Taylor et al19 reported 6 uterine ruptures (10.3%) in 58 in patients who underwent labor induction using a prostaglandin E2 vaginal insert. They reported that the average starting cervical dilatation was less than 1 cm. Because an unfavorable cervix status has been associated with prolonged labor and high intrauterine pressure20 and prolonged dystocia is a risk factor for uterine rupture,21 we believe that more data are necessary to determine whether an increased risk of uterine rupture is due to the use of prostaglandins or due to (or modified by) an unfavorable cervical status. Because of the possible association between the use of prostaglandins and an increased risk of uterine rupture, it may be more prudent to use transcervical Foley catheter when cervical ripening is required in patients with a previous cesarean delivery.
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