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ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, Virginia Commonwealth University Medical Center, Richmond, Virginia.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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METHODS: Women who presented for induction of labor with Bishop score less than 5 were randomly assigned to receive Foley alone or Foley with extra-amniotic saline infusion for induction of labor. Primary outcome was time from start of induction to vaginal delivery. Secondary outcomes were cesarean delivery rates, incidence of chorioamnionitis, Apgar scores at 1 and 5 minutes, and adverse events.
RESULTS: One hundred forty women completed the study. Time from induction to vaginal delivery was 16.58 (± 7.55) hours in the extra-amniotic saline infusion group compared with 21.47 (± 9.95) hours in the Foley group (P < .01). Chorioamnionitis occurred in 4 of 66 (6.1%) women in the extra-amniotic saline infusion group compared with 12 of 74 (16.2%) women in the Foley group (P = .067). Cesarean delivery rate was 21.2% versus 20.1% in the extra-amniotic saline infusion and Foley groups, respectively (P = 1.0). Median 1-minute and 5-minute Apgar scores were 9 in both groups. Adverse events were rare and unrelated to method of induction.
CONCLUSION: Induction of labor by using Foley with extra-amniotic saline infusion results in shorter induction-to-vaginal-delivery time than Foley alone, without affecting cesarean delivery rates.
LEVEL OF EVIDENCE: II-1
Multiple cervical ripening agents, both mechanical and pharmacological, have been studied in an attempt to determine the most effective method. Several studies show mechanical ripening with a Foley bulb to be at least as effective as other methods of ripening, with no increase in maternal or fetal morbidity. Some of these studies describe placing the Foley bulb beyond the internal cervical os and inflating it with 30–50 mL of sterile water, whereas others supplement Foley bulb placement with an extra-amniotic saline infusion at 30–40 mL/hour through the catheter. Although these methods are similar, it is possible that the addition of extra-amniotic saline may alter the mechanics of cervical ripening. The constant infusion could increase prostaglandin release, thereby shortening time of labor. Alternatively, the saline infusion could contaminate the choriodecidual space with vaginal flora and thus increase the risk of chorioamnionitis as postulated by Levey and colleagues.14 Our goal was to perform a randomized controlled trial comparing a Foley balloon alone with a Foley balloon with extra-amniotic saline infusion for induction of labor in patients with an unfavorable cervix.
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MATERIALS AND METHODS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Women who consented to participate and enrolled in the study had the following data recorded: indication for induction, age, race, gravidity, parity, estimated gestational age, and Bishop score. They were then randomly assigned to Foley alone or Foley with extra-amniotic saline infusion. A group of medical students uninvolved in the study generated a randomization sequence by shuffling cards in 2 blocks of 100 (50 Foley and 50 extra-amniotic saline infusion in each block) and placing them in sequentially numbered opaque envelopes, which were kept in the work room on the Labor and Delivery unit. Residents working on Labor and Delivery determined eligibility, enrolled subjects, collected and recorded data, and assigned treatment group according to the designation in the next consecutive envelope. Allocation to treatment group occurred upon subject agreement to participate but was concealed from participants until time of Foley placement. No one was blinded to group assignment.
Patients assigned to the Foley group had a 30F Foley catheter inserted through the cervix, outside the chorioamnion into the lower uterine segment via sterile speculum examination after Betadine preparation. The bulb was then inflated with 50 mL of sterile water and the catheter taped without tension to the medial aspect of the patient’s thigh. Standard oxytocin infusion was begun immediately per Labor and Delivery protocol. The Foley was removed 12 hours after insertion, unless rupture of membranes occurred (at which time Foley was removed) or the bulb was expelled spontaneously. The remainder of the induction process proceeded according to the standard management of labor currently employed in Labor and Delivery.
Patients assigned to the extra-amniotic saline infusion group underwent the same management, including Foley placement and oxytocin infusion as outlined above. In addition, they received infusion of room-temperature normal saline through the catheter port of the Foley at 40 mL/hour by intravenous infusion pump, beginning immediately after insertion of the catheter and continuing until the catheter was removed or expelled. Subjects in whom a Foley could not be placed were induced using misoprostol, oxytocin, or both.
The primary outcome measure was induction-to-vaginal-delivery time (defined as time from Foley insertion or first intervention to vaginal delivery). Secondary outcome measures were cesarean delivery rate, incidence of chorioamnionitis (defined as intrapartum temperature > 100.4°F without evidence of extra-uterine source), Apgar scores at 1 and 5 minutes, and adverse events.
Power analysis was performed by using institutional data from inductions using Foley alone. Based on a mean time to delivery of 20 hours with standard deviation of 8 hours, we estimated that 120 total subjects (60 per group) would be needed to detect a 4-hour difference (a 20% reduction) in induction-to-vaginal-delivery time, with a power of 80% and 
of 0.05 (2-tailed).
The GraphPad Prism (GraphPad Software, San Diego, CA) software package was used for all planned data analysis. Categorical variables were analyzed by either the 
2 or Fisher exact tests. Continuous variables were analyzed by the parametric t test. Ordinal variables were analyzed with the Mann-Whitney U test. Exploratory multivariate analyses were performed with JMP statistical software (SAS Institute, Cary, NC). All analyses were 2-tailed, with a significance level of P < .05.
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RESULTS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Mean time from induction to vaginal delivery (Table 2) was significantly shorter in the extra-amniotic saline infusion group. Cesarean delivery did not differ between the groups, nor did median 1- and 5-minute Apgar scores or 5-minute Apgar scores less than 7. Although a smaller percentage of patients in the extra-amniotic saline infusion group developed chorioamnionitis, this difference did not reach significance.
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Adverse events were rare, but included 1 case of neonatal sepsis, 2 emergent cesarean deliveries (one for breech presentation discovered during the second stage of labor and the other for cord prolapse), and 1 case of postpartum sepsis resulting in adult respiratory distress syndrome, long admission to the medical respiratory intensive care unit, and eventual hysterectomy. All 4 of these patients were in the Foley group. There were 5 cases of postpartum hemorrhage, 3 in the extra-amniotic saline infusion group (one requiring transfusion) and 2 in the Foley group (one requiring transfusion) (relative risk [RR] 1.69, 95% confidence interval [CI] 0.29–7.8, P = .89).
Because 14 subjects were found not to meet predefined inclusion criteria after enrollment, randomization, and group allocation, we reanalyzed the data excluding these subjects. Induction-to-vaginal-delivery times were similar to those of subjects included in the initial analysis: 16.23 hours in the extra-amniotic saline infusion group versus 22.19 hours in the Foley group (P < .01). Cesarean delivery occurred in 13 of 61 (21.3%) women in the extra-amniotic saline infusion group compared with 15 of 65 (23.1%) women in the Foley group (P = .81, RR 0.92, 95% CI 0.48–1.78). The incidence of chorioamnionitis was 4.9% (3 of 61) in the extra-amniotic saline infusion group and 18.5% (12 of 65) in the Foley group (P = .026, RR 0.27, 95% CI 0.08–0.90).
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DISCUSSION |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The finding of an approximately 5-hour shorter induction-to-vaginal-delivery time differs from that of a similar study published in 2004 by Guinn et al,15 which found no statistically significant difference in induction-to-vaginal-delivery time (15.0 versus 16.3 hours in extra-amniotic saline infusion compared with Foley, respectively, P = .98). Although it is unclear why our results differ, it is possible that the slightly higher infusion rate (40 mL/hour compared with 30 mL/hour) in our study played a role. In the Guinn study, the Foley was placed on tension. We chose not to apply tension to the Foley because of our inability to standardize the amount of tension. It is possible that applying tension to the Foley has an effect on time to delivery.
In our intent-to treat analysis, we found a trend toward decreased incidence of chorioamnionitis in the extra-amniotic saline infusion group that was not statistically significant. When we analyzed our data, excluding the subjects who did not meet inclusion criteria, this difference reached statistical significance. Guinn et al15 found no difference in chorioamnionitis in their study (12% in extra-amniotic saline infusion versus 10% in Foley, P = .80).
Exploratory logistic regression analysis was performed to further evaluate the relationship among induction time, method of ripening, and incidence of chorioamnionitis. We found that increased induction-to-delivery time was significantly correlated with increased risk of chorioamnionitis (P = .019). The trend toward decreased chorioamnionitis, however, did not disappear when controlling for induction-to-delivery time (odds ratio 0.40, 95% CI 0.10–1.25, P = .13). Therefore, we cannot exclude the possibility of other contributing factors.
The evidence from our study and the Guinn study seems to directly refute the findings of a retrospective cohort study by Levey et al.14 They found that extra-amniotic saline infusion increased the risk of chorioamnionitis compared with induction of labor with "other" methods and spontaneous labor and concluded that it was the infusion of saline into the extra-amniotic space that caused this increase. The only randomized trials to date comparing extra-amniotic saline infusion with Foley demonstrate no increase in chorioamnionitis with extra-amniotic saline infusion.
One limitation of our study was the inclusion of 14 subjects who did not meet predefined study criteria. The admitting residents in some cases overlooked study exclusion criteria. In other cases, a reassessment of Bishop score at the time of Foley placement by a more senior resident revealed a more favorable cervix than initially thought. Because the postrandomization discovery of subject ineligibility is not likely to be random, excluding the subjects who were found to be ineligible after randomization could bias our results.16 Therefore, we included these subjects in our data analysis. Although our secondary analysis excluding these ineligible subjects agreed, the significantly lower incidence of chorioamnionitis cannot be assumed, given the potential for bias.
With respect to cesarean section and Apgar scores, our data agree with published data and demonstrate no significant difference in the extra-amniotic saline infusion group compared with Foley. Given the small sample size, however, our study is underpowered to detect a true difference. Power analysis determined that, to detect an increase in cesarean delivery from 20% to 25%, we would need 1,133 subjects per group, assuming power of 80% and of 0.05. Likewise, to detect a change in 5-minute Apgar scores less than 7 from 3% to 1.5%, we would need 1,664 subjects per group. Given the large numbers required to fully examine these secondary outcomes, they would be best evaluated by a large-scale, multicenter trial and are beyond the scope of the current study.
Although 4 significant adverse events did occur in the Foley group, they were too few and diverse to analyze statistically. Furthermore, these events are thought to be unrelated to the method of induction. Postpartum hemorrhage did occur in 5 of 140 subjects (3.6%), which is similar to the incidence in previously reported studies and did not differ significantly between study groups.
We believe that extra-amniotic saline infusion through a transcervical Foley catheter at 40 mL/hour should be strongly considered for induction of labor in patients with an unfavorable cervix because it may result in shorter induction-to-vaginal-delivery time than Foley alone.
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Footnotes |
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doi:10.1097/01.AOG.0000198629.44186.c8
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REFERENCES |
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2. Vrouenraets FP, Roumen FJ, Dehing CJ, van den Akker ES, Aarts MJ, Scheve EJ. Bishop score and risk of cesarean delivery after induction of labor in nulliparous women. Obstet Gynecol 2005;105:690–7.
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15. Guinn DA, Davies JK, Jones RO, Sullivan L, Wolf D. Labor induction in women with an unfavorable Bishop score: randomized controlled trial of intrauterine Foley catheter with concurrent oxytocin infusion versus Foley catheter with extra-amniotic saline infusion with concurrent oxytocin infusion. Am J Obstet Gynecol 2004;191:225–9.[Medline]
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  M. G. Lin, K. J. Reid, M. R. Treaster, F. S. Nuthalapaty, P. S. Ramsey, and G. C. Lu Transcervical Foley Catheter With and Without Extraamniotic Saline Infusion for Labor Induction: A Randomized Controlled Trial Obstet. Gynecol., September 1, 2007; 110(3): 558 - 565. [Abstract] [Full Text] [PDF]
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