Labor induction is one of the most frequently used procedures in obstetrics. The incidence of labor induction has increased “significantly” in the past decade, with elective induction of labor becoming a “significant” contributor to the increasing induction rate.1,2 The ideal methods for cervical ripening are those that are safe for both the mother and fetus, incur a low cost, have minimal maternal discomfort, and do not require extensive monitoring. A wide variety of methods are available. These methods may be divided into pharmacological and mechanical methods.2,3
Foley catheter balloon has been established as a safe and effective mechanical method for labor induction.2 Comparison between transcervical Foley catheter and prostaglandins (pharmacological agents) did not reveal a significant difference in the duration of induction to delivery or in the risk of cesarean delivery;2 however, Foley catheter use decreases the risk of uterine tachysystole (with or without fetal heart rate changes) and offers the advantage of lower cost, reversibility, and stability at room temperature.3–5
Compared with the Foley catheter, which has a single balloon, a double-balloon catheter has been described to have an additional utility in the unripe cervix by applying pressure on both the external os and internal os.6 Although Atad et al6 suggested an extra mechanism of action with a single balloon, a comparison in terms of efficacy between the two catheters and the superiority of this additional mechanism still need to be confirmed in randomized trials. The present study was undertaken to compare the efficacy of a double-balloon catheter compared with a single-balloon catheter among women with an unfavorable cervix.
MATERIALS AND METHODS
This prospective randomized study was conducted at a university teaching medical center between June 2008 and December 2010. Women eligible for inclusion had a fetal or maternal indication for induction of labor, a viable singleton pregnancy, cephalic presentation, intact membranes, and a Bishop score of 6 or less. Exclusion criteria were any contraindication for vaginal delivery, a previous cesarean delivery, a low-lying placenta defined as placental edge less than 2 cm from the internal os as measured by ultrasonography, fetal malformations diagnosed in the antepartum period that were incompatible with postpartum life, intrauterine fetal death, clinical amnionitis, women who were carriers of hepatitis B or C or human immunodeficiency viruses, and women with a history of allergy to latex.
Maternal indications for induction of labor included hypertensive disorders, diabetes in pregnancy, postterm pregnancy, thrombophilia, and women's request. Fetal indications included intra uterine growth restrictions, oligohydramnios, nonreassuring fetal status, and estimated large-for-date fetus. Women were given information about the trial when the decision was made to induce labor with a balloon catheter. Informed consent was obtained.
Women recruited to the study were randomized to one of the following cervical ripening catheters. In group 1, a single-balloon catheter was used. A 24-French Foley catheter (Unomedical Sdn Bhd) was inserted above the internal cervical os and filled with 60 mL of normal saline. The catheter was strapped to the inner aspect of one leg after tension. In group 2, a double-balloon catheter was used. A double-balloon catheter (Cook Cervical Ripener Balloon, Cook OB/GYN) was inserted through the cervix, and balloons on either side of the cervix were inflated with 80 mL of normal saline in accordance with the recommendations from the manufacturer. The catheter was taped to the inner thigh, without tension, for patient comfort, because the two balloons place pressure on the cervical os. Other than the catheter type, the remainder of the cervical ripening process and labor induction management were identical for the two treatment groups.
Placement of the catheters was performed by the digital or speculum method depending on clinician preference after cleaning the cervix with antiseptic solution, and proper placement of the catheter was confirmed with digital examination. Each catheter insertion was supervised by a trial investigator. Nonstress test was conducted after catheter insertion. Removal of the catheter was planned at approximately 12 hours after insertion if spontaneous expulsion had not occurred. Artificial rupture of the membranes and oxytocin infusion was commenced if labor did not begin spontaneously after removal or spontaneous expulsion of the catheter. Continuous electronic fetal monitoring was used throughout established labor. Labor was managed by the attending obstetricians and midwives. Labor progress abnormalities were diagnosed and managed according to the recommendations of the American College of Obstetricians and Gynecologists.7 Failed induction of labor was defined as failure to progress to the active phase 12 hours after water breakage combined with oxytocin. When operative vaginal delivery was applied, only vacuum extraction was used and it was performed when the fetal position was 2 cm lower than the level of the ischial spines. Analgesia was administered at maternal request according to the unit protocol. Management was standardized regardless of the catheter type.
The primary outcome was time duration from insertion of the catheter until delivery. Secondary outcome was mode of delivery. In addition, the proportion of vaginal deliveries within 24 hours from catheter insertion with adverse events defined as the occurrence of one or more of the following were also examined: abnormal fetal presentation, cord prolapse, intrapartum fever more than 38°C, and bleeding related to catheter insertion that required removal of the catheter and Apgar score.
Randomization of the groups was performed in blocks of 10 using a computer randomization sequence generation program, and the randomization results were kept in the labor and delivery ward in a closed study box. The sequence was concealed until intervention was assigned, ie, just before catheter placement. Blinding of participants or care providers was not performed. All authors took part in enrolling and assigning women to interventions.
The study was approved by the local Institutional Review Board and the Israeli ministry of health. Each woman signed an informed consent.
To test the differences between the two types of the catheters, categorical variables were analyzed by χ2 test or Fisher exact test when warranted. Independent t test or the Mann-Whitney U test, in the case of nonnormally distributed variables, was used to test differences between the two types of balloon for the continuous variables. The Kolgomov-Smirnov test was used to test for normality of the continuous variables. The analysis was then repeated for primiparous and multiparous women separately. The demographic and obstetrical outcomes were similarly compared for deliveries in which there was spontaneous expulsion as opposed to deliveries in which there was planned removal of the catheters. Relative risks and the associated 95% confidence intervals were computed using spontaneous expulsion as the reference group. In the case of continuous variables, odds ratios derived from univariate logistic regression were used as an estimate of the relative risk.
Power analysis was based on time from induction to delivery according to previous reports describing the mean time from induction to delivery of the double-balloon catheter (17.7 and 18.9 hours) and the single-balloon catheter (20.03 hours).6,8,9 To be 95% confident (α=0.05) of detecting a difference of 2 hours with 80% power, a sample size of 145 women in each group was needed assuming a standard deviation of 6 hours.
Over the course of the study period, 368 women were eligible for inclusion into the study and were invited to participate. Sixty-six women declined. Of the 302 women recruited, three women elected to discontinue their induction during catheter insertion, two women had spontaneous contractions develop and a cervical progression was confirmed just before the insertion of the catheter, one woman recruited to group 2 demanded removal of the catheter soon after insertion because of discomfort, and among three women a delay in the catheter removal occurred because of a high burden in the delivery ward. Thus, 293 women had complete data available for statistical analysis of the primary outcome (145 women in group 1 and 148 in group 2; Fig. 1).
Both groups had similar baseline demographic and obstetric parameters (Table 1). After catheter insertion, 54 (37.2%) and 70 (47.3%) women had a spontaneous expulsion of the catheter among group 1 and group 2, respectively (P=.1). Of the remaining women, the mean time from insertion until planned removal of the catheter was 11.3 (±2.6) and 11.1 (±2.8) hours among groups 1 and 2, respectively (P=.56). The mean increase in Bishop score after catheter removal was 2.94 (±1.91) and 3.21 (±2.04) among groups 1 and 2, respectively (P=.06). The mean length of time from insertion until delivery was not significantly different between the two groups (Table 2). The incidence of vaginal and cesarean deliveries did not differ between the groups; however, the incidence of operative deliveries (vacuum or cesarean) was significantly higher in group 2 compared with group 1 (P=.02; odds ratio 0.49, 95% confidence interval 0.26–0.92; Table 2). Two women in group 2 had a fetal malpresentation after the catheter removal. The first had a face presentation and underwent operation because of persistent mento-posterior presentation. The second woman had a fetus with a transverse lie after removal of the catheter. An external cephalic version was performed successfully and this woman delivered vaginally. One woman in group 2 had an emergency cesarean delivery because of cord prolapse. There were no cases of bleeding related to catheter insertion that required removal of the catheter. Intrapartum fever developed in two (1.4%) and eight (5.4%) women among groups 1 and 2, respectively (P=.10). The incidence of composite adverse events was significantly lower among group 1 compared with group 2 (P=.02; odds ratio 0.17, 95% confidence interval 0.04–0.80; Table 2).
Mean number of maternal hospitalization days subsequent to delivery was 3.46 (±1.53) and 3.48 (±1.55) days in groups 1 and 2, respectively (P=.91). Eleven newborns were admitted to the neonatal intensive care unit, seven (4.8%) in group 1 and four (2.7%) in group 2 (P=.37). One newborn in group 2 had culture-proven sepsis.
We furthered subanalyzed the results according to parity. Demographic data of primiparous and multiparous women were comparable between the groups. The mean length of time from insertion until delivery was not significantly different between the two groups regardless of parity (Table 3).
Of all 293 women recruited, 124 (42.3%) had a spontaneous expulsion of the catheter and in 169 (57.7%) the catheter was removed intentionally. The incidence of spontaneous expulsion did not differ between the groups (Table 4). Women who had a spontaneous expulsion of the catheter demonstrated a favorable outcome in terms of a shorter time from induction to delivery and a significantly lower proportion of operative deliveries (Table 4).
The present study was undertaken to compare the efficacy of a double-balloon catheter compared with a single-balloon catheter among women with an unfavorable cervix undergoing labor induction. Both catheters were comparable in term of length of time from induction to delivery regardless of parity. The incidence of vaginal compared with cesarean delivery was also comparable between the groups; however, a significantly higher proportion of women induced with a double-balloon catheter delivered operatively than did women induced with a single-balloon catheter. Observed composite adverse events that included intrapartum fever, malpresentation, and cord prolapse were significantly higher among women who had a double-balloon catheter compared with a single-balloon catheter. None of the neonates had an Apgar score less than 7 at 5 minutes. Women who had a spontaneous expulsion of the catheter regardless of the catheter type demonstrated a favorable outcome in terms of a shorter time from induction to delivery and a significantly lower proportion of operative deliveries.
Labor induction is one of the most frequent procedures performed in obstetrics. The incidence of labor induction has increased significantly in the past decade.1,2 Many methods are used to ripen the cervix; however, there is little consensus on the best method.10–14 It is suggested that ripening efficacy by catheter balloon is comparable or better (less uterine tachysystole) than pharmacological methods, with no significant difference in the mode of delivery or perinatal outcome. The single-balloon catheter has the advantages of simplicity, low cost, reversibility, and lack of systemic or serious side effects.15 The proposed mechanism of cervical ripening by extra-amniotic Foley catheter balloon consists of a direct stretching of the balloon on the cervix and lower uterine segment and secretion of prostaglandins by a separation and stripping of the membranes.16–18
Compared with the Foley catheter, which has a single balloon and incurs a lower cost, a double-balloon catheter has been described to have an additional mechanism of action on the unripe cervix that is achieved by the pressure being applied on both the external and internal os.6 According to Atad et al,6 the advantage of the double-balloon catheter is that it is held in place and the dilator vector is applied by the two balloons inflated on both sides of the cervix, avoiding the need for traction. Moreover, Atad et al6 reported that the mean increase in Bishop score after utilizing a Foley catheter, as reported by the literature, was lower than that achieved by the double-balloon catheter, with a higher failure rate than the double-balloon catheter. According to the results of the current study, the mean increase in Bishop score after catheter removal was similar between the two catheters and the time from catheter insertion until delivery was also comparable. In addition, the rate of cesarean deliveries did not differ between the groups. This observation is consistent with the results of Pennell et al,19 who compared between the two catheters, in addition to prostaglandin estradiol gel, and described comparable outcomes.
Although the rate of abdominal compared with vaginal deliveries was comparable between the two catheters in this study, we observed a significantly lower rate of operative deliveries among the single-balloon group compared with the double-balloon group. In addition, we observed that the incidence of operative deliveries attributable to failure to progress was approximately two-times higher among the double-balloon catheter compared with the single-balloon catheter, although this difference was not significant. These observations were not reported by Pennell et al;19 however, compared with their study in which 30 mL was used to inflate the single-balloon catheter, we inflated the Foley catheter with 60 mL. It has been reported from previous studies that inflation of a transcervical Foley balloon for induction of labor to 60 mL or 80 mL is a more effective method of labor induction as compared with inflation to 30 mL.5,18,20 If this observation is accurate, then it may be attributed to the traction mechanism required with the single-balloon catheter and abandoned with the double-balloon catheter in accordance with the recommendations from the manufacturer. Traction applies a stretching pressure on the lower uterine segment, which has been described as one of the mechanisms for cervical ripening.15 This traction may have a greater effect on labor pattern than that applied by the two balloons inflated on both sides of the cervix, avoiding the need for traction. However, this study was not designed to investigate this difference between the catheters and only future studies may confirm this suggestion.
The limitations of the current study are worth mentioning. First, blinding was not performed among patients and providers. However, other than the catheter type, management was standardized. Accordingly, such unblinding is not expected to affect the objectively measured outcomes such as length of labor or mode of delivery and probably the clinical decision process regarding labor management. Second, although we conducted a priori sample size calculation to ensure adequate power to examine length of labor from induction to delivery, we may be underpowered to detect small differences in terms of secondary outcomes. Last, a proportion of women received prostaglandin estradiol before catheter insertion. None had a concomitant use of prostaglandins with the catheter. In addition, its use was evenly distributed across both study arms and the Bishop score was comparable before catheter insertion. Thus, prostaglandin use could not have contributed to a confounding bias.
In conclusion, the results suggest that either catheter is equally efficacious for inducing labor. However, the results also demonstrate some worrying trends toward increased adverse events and more operative deliveries with the double-balloon catheter. These findings, coupled with fact that each double-balloon catheter costs our medical center $37 compared with $0.60 for the single-balloon catheter, make the single-balloon Foley catheter a more cost-effective method for labor induction.
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© 2011 The American College of Obstetricians and Gynecologists
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