Background
Induction of labor is common in the United States. Multiple previous studies have tried to outline a faster time to delivery to improve maternal and fetal outcomes.
Objective
This study aimed to evaluate whether women who undergo induction of labor with a single-balloon catheter and oxytocin have a shorter time to delivery with planned removal of the catheter at 6 vs 12 hours.
Study Design
In this randomized controlled trial, induction of labor was performed using a combination of single-balloon catheter and oxytocin. Term women, both nulliparous and multiparous, aged 18 to 50 years old with cephalic singletons were included if they were undergoing induction of labor with a Bishop score of <6 and cervical dilation of <2 cm. Women were randomized to planned removal of the single-balloon catheter at 6 hours vs 12 hours. The primary outcome was time from catheter insertion to delivery. We were powered to show a 4-hour time difference with a sample size of 89 women per group (n=178). Planned sensitivity analyses were performed to account for cesarean delivery in labor.
Results
From February 2019 to June 2020, 237 women were screened, 178 women were randomized, and 177 women were included in the final analysis (89 women in the 6-hour group and 88 women in the 12-hour group). Insertion to delivery time was significantly shorter in the 6-hour group (19.2 vs 24.3 hours; P =.04), and the proportion of women delivered by 24 hours was significantly greater in the 6-hour group (67.4% vs 47.4%; P <.01). There was no difference in the Bishop score at removal of the catheter or secondary maternal or neonatal outcomes. In a Cox proportional-hazards model censoring for cesarean delivery, the 6-hour group had a significantly shorter insertion to delivery time (hazard ratio, 0.67; P =.02).
Conclusion
Induction of labor with a single-balloon catheter and oxytocin with planned removal of the catheter at 6 hours rather than 12 hours results in a shorter time from insertion to delivery without increasing the rate of cesarean delivery. Decreasing the length of time a single-balloon catheter is in place should be considered in clinical protocols.
Introduction
Induction of labor (IOL) is a common practice in the United States, occurring in about 1 in 4 pregnancies, and can greatly improve maternal and fetal outcomes. , There are multiple methods for initiating cervical ripening and IOL. Use of balloon catheters is a mechanical strategy of cervical ripening, is associated with low cost and reduced risk of uterine tachysystole compared with prostaglandins, and is associated with lower rates of cesarean delivery compared with the use of oxytocin alone. , Recently, studies have demonstrated the efficacy and shorter time to delivery using dual methods, such as oxytocin along with balloon catheter placement. ,
Why was this study conducted?
No previous study with a combination of labor induction methods has analyzed outcomes following the removal of a single-balloon catheter at 6 hours.
Key findings
Induction of labor with a single-balloon catheter and oxytocin resulted in a shorter time to delivery when removed at 6 hours. In addition, women were more likely to deliver in 24 hours when the balloon catheter was removed at 6 hours. No difference in Bishop score after removal of the balloon catheter at 6 hours.
What does this add to what is known?
This study will improve the literature on combination of labor induction methods by shortening the amount of time a single-balloon catheter is in place.
Time to delivery is an important consideration during IOL because of its association with increased risk of cesarean delivery, postpartum hemorrhage, and maternal and neonatal infections. , , Moreover, a lengthy IOL process can overburden busy delivery wards, can contribute to rising healthcare costs, and is associated with lower patient satisfaction scores. Previous studies have compared balloon catheter placement for 12 vs 24 hours and demonstrated that 12 hours of balloon catheter placement is associated with shorter time to delivery and higher rates of vaginal deliveries. , Recently, the first randomized controlled trial (RCT) comparing a double-balloon catheter placement for 6 vs 12 hours was published, revealing faster time to delivery with adequate cervical ripening. However, none of these previous studies included dual labor induction methods.
The purpose of this study was to evaluate whether time to delivery is shorter for women who undergo an IOL with a single-balloon catheter and oxytocin with planned removal of the catheter at 6 hours vs 12 hours.
Materials and Methods
We conducted this RCT at a single tertiary care center. Before the initiation of the study, approval was obtained from a convened institutional review board (identification number 2018P000061, approved on 4/6/2018). Furthermore, this study is registered on ClinicalTrials.gov (National Clinical Trial identifier 04233008).
Participants were at least 18 years of age with a term (37 0/7 to 41 6/7 weeks’ gestation) singleton in cephalic presentation. Both nulliparous and multiparous women were included. Women were required to have intact membranes, a Bishop score of ≤6, and a cervical of dilation ≤2 cm to be eligible. Women were excluded if there was a contraindication to a vaginal delivery or previous cesarean delivery. Non–English-speaking women were also excluded.
Participants were approached as outpatients or on admission to labor and delivery by healthcare providers trained in the consenting process before the start of their induction. After written consent was obtained, a cervical examination was performed by healthcare providers on labor and delivery, and an intracervical Cook double-balloon catheter (Cook Medical, LLC, Bloomington, IN) was placed, but only the single intrauterine balloon was inflated with 60 mL normal saline. Our institution routinely uses Cook catheters as providers routinely prefer the stylet for insertion. Placement of the catheter was left at the discretion of the labor and delivery provider and could be attempted blindly or with a speculum. Betadine preparation is not routinely used at our institution. The balloon catheter was taped to the maternal leg and placed on tension. Patients were then randomized to either the 6- or 12-hour group with single-balloon catheter and oxytocin. An independent consultant created a computer-generated randomization scheme that used balanced treatment allocation in blocks of 10, and the resulting sequential group allocations were kept in sealed, opaque envelopes until the time of randomization. Neither the patients nor the healthcare providers were blinded to the assigned treatment group.
Within an hour after catheter placement, participants in both groups were started on the same hospital-based oxytocin protocol beginning at 2 mU/minute and increasing by 2 mU with a maximum dose of 30 mU as tolerated by the mother and fetus. The single-balloon catheter was removed at 6 or 12 hours if spontaneous expulsion or rupture of membranes (ROM) did not occur before then, and a Bishop score was obtained. Following the removal of the single-balloon catheter, management of active labor was at the discretion of the healthcare providers. Amniotomy could be performed at any point, with the recommendation that it be performed when the cervix was dilated at >4 cm. Other labor interventions, such as operative delivery or cesarean delivery, were at the discretion of the healthcare provider.
The primary outcome was the length of time (hours) from a single-balloon catheter insertion to delivery. Secondary outcome measures included cesarean delivery rate, time to vaginal delivery (hours), time to active labor (defined as dilation ≥6 cm), delivery within 12 hours, delivery within 24 hours, time (hours) with a single-balloon catheter in place, change in Bishop score during the intervention, and indication for cesarean delivery. Other secondary outcomes included potential markers for maternal morbidity, including chorioamnionitis, higher-order laceration, postpartum hemorrhage (defined as estimated blood loss >1 L), blood transfusion, endometritis, wound infection, hysterectomy, intensive care unit (ICU) admission, readmission, and postpartum length of stay. Neonatal outcomes included birthweight, 1- and 5-minute Apgar scores, neonatal intensive care (NICU) admission (excluding anomalies), NICU admission of >48 hours (excluding anomalies), length of stay, and culture-proven neonatal sepsis.
Outcome measures were defined by the clinical providers on labor and delivery at the time of the IOL. Chorioamnionitis was defined clinically by the providers on labor and delivery but, in general practice at our institution, is defined as a temperature of >100.4°F with the presence of maternal leukocytosis, purulent cervical discharge, or maternal or fetal tachycardia. The indications for cesarean delivery were also left to the discretion of the provider. In general, our labor floor follows the National Institutes of Health guidelines for preventing the first cesarean delivery.
All IOL and labor and delivery information, maternal demographics, and secondary outcomes were collected by review of the medical record by a study team member who was blinded to group allocation.
A 4-hour difference in time to delivery was considered clinically meaningful, consistent with previous literature, and an average IOL length of 18.5±8.5 hours for women with a 12-hour balloon catheter was assumed. A type 1 (α) error of 0.05 was selected. Assuming 80% power, equal group sizes, and a 2-sided P value, we needed 71 women per arm. Assuming that 20% of women would have a cesarean delivery in labor, we planned to randomize 89 women in each arm (leaving 71 with a vaginal delivery) for a total of 178 women. In addition, we planned to analyze the data using survival analysis with a Cox proportional-hazards model censoring for cesarean delivery.
Demographic and clinical characteristics were compared using the Fischer exact and chi-square tests where appropriate. Continuous variables were assessed for normality, and t tests or Wilcoxon rank-sum tests were used as appropriate. Univariate analyses for outcomes were performed similarly with the Fischer exact tests, chi-square tests, and Wilcoxon rank-sum tests where appropriate. The distribution of time to delivery was modeled using a survival method. Labor length with censoring for cesarean delivery was also modeled using a Cox proportional-hazards model. Hazard ratios (HRs) and risk ratios with 95% confidence interval (CI) are reported. For all analyses, a 2-sided significance level of P <.05 was considered statistically significant. Analyses were performed using the Statistical Analysis System software (version 9.3; SAS Institute Inc, Cary, NC).
Results
A total of 237 women were approached for participation from February 2019 to June 2020 ( Figure 1 ). However, 59 women either declined participation or were excluded (as they no longer met the inclusion criteria because of a more favorable cervix by the time they presented for IOL). Therefore, 178 women were randomized. Notably, 1 woman in the 12-hour group was withdrawn from analysis following randomization, as she was discharged home after her catheter came out and her cervix was still unfavorable, yielding a final sample size of 177 women. There was no withdrawal or patient lost to follow-up.
There was no notable difference in the groups with respect to baseline characteristics ( Table 1 ).
| Characteristic | 6-h group (n=89) | 12-h group (n=88) |
|---|---|---|
| Age (y) | 31.2 (28.4, 33.1) | 31.4 (29.0, 36.1) |
| BMI at delivery (kg/m 2 ) | 30.1 (26.4, 34.1) | 31.8 (27.5, 36.1) |
| Gestational age (wk) | 39.0 (38.3, 39.7) | 39.0 (37.7, 39.1) |
| Nulliparous | 71 (79.8) | 68 (77.3) |
| Fetal anomaly | 15 (16.9) | 9 (10.2) |
| Race | ||
| White | 43 (48.3) | 52 (59.1) |
| Latinx | 20 (22.5) | 12 (13.6) |
| Black | 16 (18.0) | 18 (20.5) |
| Asian | 8 (9.0) | 6 (6.8) |
| Other | 2 (2.3) | 0 |
| Maternal comorbidity | ||
| Gestational diabetes mellitus | 11 (12.4) | 14 (15.9) |
| Pregestational diabetes | 5 (5.6) | 5 (5.7) |
| Chronic HTN | 10 (11.2) | 12 (13.6) |
| Gestational HTN | 13 (14.6) | 16 (18.2) |
| Preeclampsia with severe features | 3 (3.4) | 8 (9.1) |
| Tobacco use | 3 (3.4) | 3 (3.4) |
| Bishop score at randomization | 2 (1, 3) | 2 (1, 3) |
| Dilation at randomization | 1 (0, 1) | 1 (0, 1) |
| Indication for induction of labor | ||
| Late-term or postterm pregnancy | 3 (3.4) | 4 (4.6) |
| Maternal | 42 (47.2) | 52 (59.1) |
| Fetal | 18 (20.2) | 19 (21.6) |
| Elective | 26 (29.2) | 13 (14.8) |
| Epidural use | 88 (98.9) | 84 (95.5) |
| Birthweight (g) | 3200 (2905, 3600) | 3149 (2797, 3512) |
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