Introduction
Induction of labor is becoming an increasingly common practice in obstetrics, now making up approximately 20% of all births. Induction of labor in the setting of an unfavorable cervix may lead to longer lengths of stay, increased hospital costs, and/or increased maternal or neonatal morbidities. To mitigate these risks, it is important to choose induction methods that are safe and efficient in achieving a vaginal delivery.
Cervical ripening prior to induction with oxytocin in women with an unfavorable Bishop score increases the likelihood of a vaginal delivery. There are a variety of mechanical and pharmacologic methods that have been studied for this purpose. Prostaglandins may be administered vaginally to mimic the natural processes that occur in the cervical tissue during labor. Mechanical ripening agents may also be used to stimulate endogenous prostaglandin production by stretching myometrial cells. Studies comparing these 2 methods have demonstrated similar efficacy and safety, however a lower rate of uterine tachysystole with fetal heart rate changes is seen with mechanical methods. Due to a low risk of adverse outcomes, mechanical dilation with a Foley balloon has come into favor and its safety and efficacy have been established.
Because cervical ripening with Foley balloon generally does not result in sustained contractions, further induction with oxytocin may be considered. There is paucity of literature guiding the timing of initiation of oxytocin. One randomized study compared simultaneous use of oxytocin and Foley balloon to sequential use of Foley balloon followed by oxytocin once the balloon was extruded. There was no difference in the proportion of deliveries that occurred in <24 hours. This study was not powered to detect a difference based on parity or in time to delivery.
The most effective induction method in terms of decreasing time to delivery in nulliparous women with an unfavorable cervix remains unknown. Maximizing likelihood of successful vaginal delivery in this population is important and potentially has long-term impact on maternal morbidity. The aim of this study was to determine whether simultaneous use of Foley balloon inflated to 60 mL and oxytocin decreases time to delivery in nulliparous women compared to the sequential use of Foley balloon followed by oxytocin.
Materials and Methods
A randomized clinical trial of nulliparous women presenting for induction of labor at Mount Sinai Hospital, New York, NY, from December 2013 through March 2015 was conducted to determine whether simultaneous vs sequential use of Foley balloon with oxytocin decreases induction time to delivery.
Nulliparous women ≥24 weeks’ gestational age; with a live, nonanomalous singleton fetus in vertex presentation; with an initial cervical dilation <3 cm; who were admitted for induction of labor for indications determined by their primary provider; and in whom cervical ripening with Foley balloon was planned were eligible for enrollment. Patients with prior uterine surgery, unexplained vaginal bleeding, latex allergy or any contraindication to vaginal delivery were ineligible.
Eligible women were identified by the labor and delivery staff and approached regarding their interest in hearing about this study. Patients who were interested were then approached by study personnel and counseled on the risks and benefits of participation. Patients were informed that their participation was voluntary and that choosing not to participate in the study would not affect their care.
After signing informed consent, participants were randomized using previously prepared envelopes. The randomization envelopes were prepared prior to the start of the study using a random number generator from OpenEpi, Version 3 (Emory University, Atlanta, GA). Cards allocating patients to either oxytocin or no oxytocin groups were placed in 170 sealed, opaque, numbered envelopes. After signing informed consent, participants were then given the next envelope.
After enrollment, each patient had a transcervical Foley balloon placed in a standard, sterile fashion. A 16F 30-mL balloon was used in each case and inflated to 60 mL with normal saline. Proper placement of the Foley balloon was confirmed by digital or ultrasound exam in all patients. The end of the Foley catheter was taped under tension to the patient’s inner thigh.
For those patients assigned to the simultaneous group, oxytocin was started within 1 hour of insertion of the Foley balloon and titrated according to the Icahn School of Medicine at Mount Sinai institutional protocol. Oxytocin infusion was started at 2 mU/min. This dose was doubled every 30 minutes to a maximum dose of 16 mU/min (2-4-8-16) and then could be increased by 2 mU/min every 30 minutes to a maximum dose of 30 mU/min. Fetal heart rate and contraction patterns were monitored continuously in patients receiving oxytocin.
For patients assigned to the sequential group, oxytocin was started within 1 hour of spontaneous expulsion of the balloon using the above institutional protocol. If spontaneous expulsion did not occur, the Foley balloon was removed after 12 hours of cervical ripening. For all patients, the remainder of the patient’s labor was managed by the primary provider in accordance with standard obstetric practice.
Sample size was determined based on time from induction to delivery. A calculation with 80% power (alpha 0.05) was performed, which determined that 55 patients in each arm were needed to detect a 20% difference in time to delivery. Additional patients were recruited to account for study dropout, incomplete charts, or inadvertent study crossover. Secondary outcomes included cesarean delivery rate, rates of chorioamnionitis, estimated blood loss, rates of postpartum hemorrhage, and a composite neonatal outcome.
Both intention-to-treat (ITT) and per protocol analyses were performed; however since they were in agreement, only results from the ITT analysis are presented. The mean and SD or median and range are presented for quantitative variables, and frequency and percentage for qualitative variables, with comparisons between randomization groups made using the Student t test or Wilcoxon rank sum test and χ 2 test, respectively. All hypothesis testing was 2-sided and conducted at the 5% level of significance. Analyses were performed using SAS, Version 9.4 (SAS Institute, Cory, NC).
This study was approved by the institutional review board of the Mount Sinai Hospital (Grants and Contracts Office no. 13-1279) and is registered at clinicaltrials.gov (NCT02098421).
Materials and Methods
A randomized clinical trial of nulliparous women presenting for induction of labor at Mount Sinai Hospital, New York, NY, from December 2013 through March 2015 was conducted to determine whether simultaneous vs sequential use of Foley balloon with oxytocin decreases induction time to delivery.
Nulliparous women ≥24 weeks’ gestational age; with a live, nonanomalous singleton fetus in vertex presentation; with an initial cervical dilation <3 cm; who were admitted for induction of labor for indications determined by their primary provider; and in whom cervical ripening with Foley balloon was planned were eligible for enrollment. Patients with prior uterine surgery, unexplained vaginal bleeding, latex allergy or any contraindication to vaginal delivery were ineligible.
Eligible women were identified by the labor and delivery staff and approached regarding their interest in hearing about this study. Patients who were interested were then approached by study personnel and counseled on the risks and benefits of participation. Patients were informed that their participation was voluntary and that choosing not to participate in the study would not affect their care.
After signing informed consent, participants were randomized using previously prepared envelopes. The randomization envelopes were prepared prior to the start of the study using a random number generator from OpenEpi, Version 3 (Emory University, Atlanta, GA). Cards allocating patients to either oxytocin or no oxytocin groups were placed in 170 sealed, opaque, numbered envelopes. After signing informed consent, participants were then given the next envelope.
After enrollment, each patient had a transcervical Foley balloon placed in a standard, sterile fashion. A 16F 30-mL balloon was used in each case and inflated to 60 mL with normal saline. Proper placement of the Foley balloon was confirmed by digital or ultrasound exam in all patients. The end of the Foley catheter was taped under tension to the patient’s inner thigh.
For those patients assigned to the simultaneous group, oxytocin was started within 1 hour of insertion of the Foley balloon and titrated according to the Icahn School of Medicine at Mount Sinai institutional protocol. Oxytocin infusion was started at 2 mU/min. This dose was doubled every 30 minutes to a maximum dose of 16 mU/min (2-4-8-16) and then could be increased by 2 mU/min every 30 minutes to a maximum dose of 30 mU/min. Fetal heart rate and contraction patterns were monitored continuously in patients receiving oxytocin.
For patients assigned to the sequential group, oxytocin was started within 1 hour of spontaneous expulsion of the balloon using the above institutional protocol. If spontaneous expulsion did not occur, the Foley balloon was removed after 12 hours of cervical ripening. For all patients, the remainder of the patient’s labor was managed by the primary provider in accordance with standard obstetric practice.
Sample size was determined based on time from induction to delivery. A calculation with 80% power (alpha 0.05) was performed, which determined that 55 patients in each arm were needed to detect a 20% difference in time to delivery. Additional patients were recruited to account for study dropout, incomplete charts, or inadvertent study crossover. Secondary outcomes included cesarean delivery rate, rates of chorioamnionitis, estimated blood loss, rates of postpartum hemorrhage, and a composite neonatal outcome.
Both intention-to-treat (ITT) and per protocol analyses were performed; however since they were in agreement, only results from the ITT analysis are presented. The mean and SD or median and range are presented for quantitative variables, and frequency and percentage for qualitative variables, with comparisons between randomization groups made using the Student t test or Wilcoxon rank sum test and χ 2 test, respectively. All hypothesis testing was 2-sided and conducted at the 5% level of significance. Analyses were performed using SAS, Version 9.4 (SAS Institute, Cory, NC).
This study was approved by the institutional review board of the Mount Sinai Hospital (Grants and Contracts Office no. 13-1279) and is registered at clinicaltrials.gov (NCT02098421).
Results
Of 190 women approached about the study, 166 were enrolled: 82 in the simultaneous and 84 in the sequential group ( Figure 1 ). The data were analyzed on an ITT basis. There were 5 patients who were randomized in this study, although they did not meet the inclusion criteria: 1 patient had premature rupture of membranes at the time of admission, 1 patient had a fetus with known fetal cardiac anomaly, 1 patient was >3 cm dilated at time of Foley balloon insertion, 1 patient was pregnant with twins, and 1 patient had a prior uterine scar from myomectomy. Two patients received the wrong intervention: 1 patient who was randomized to the simultaneous group actually had oxytocin started after expulsion of the Foley balloon and 1 patient who was randomized to the sequential group actually had oxytocin started at the time of Foley balloon insertion. All 7 of these patients were included in the data analysis. An as-treated analysis was also performed and the results were not statistically different.
Baseline demographic factors, medical or obstetric conditions, and gestational ages were similar in both groups ( Table 1 ). Additionally, there were no differences in admission Bishop score.
| Simultaneous N = 82 | Sequential N = 84 | Overall | |
|---|---|---|---|
| Maternal age, y (SD) | 29.72 (6.47) | 28.56 (7.27) | 29.13 (6.89) |
| GA at delivery, wk | 39.57 (1.80) | 39.21 (1.84) | 39.39 (1.82) |
| Admission Bishop score, median [minimum-maximum] | 1 [0-6] | 1 [0-6] | 1 [0-6] |
| BMI, n (%) | 31.84 (6.57) | 30.52 (5.29) | 31.17 (5.97) |
| Pregestational DM, n (%) | 2 (2%) | 0 (0%) | 2 (1%) |
| Gestational DM, n (%) | 8 (10%) | 6 (7%) | 14 (8%) |
| Chronic HTN, n (%) | 6 (7%) | 4 (5%) | 10 (6%) |
| Asthma, n (%) | 13 (16%) | 10 (12%) | 23 (14%) |
| Indication for induction, n (%) | |||
| Late term | 19 (22.62%) | 22 (27.5%) | 41 (25%) |
| Gestational HTN | 27 (32.14%) | 21 (26.25%) | 48 (29.27%) |
| Preeclampsia | 4 (4.76%) | 4 (5%) | 8 (4.88%) |
| Oligohydramnios | 8 (9.52%) | 5 (6.25%) | 13 (7.93%) |
| Nonreassuring fetal status | 1 (1.19%) | 5 (6.25%) | 6 (3.66%) |
| IUGR | 2 (2.38%) | 6 (7.5%) | 8 (4.88%) |
| Elective | 3 (3.57%) | 4 (55) | 7 (4.27%) |
| ICP | 8 (9.52%) | 1 (1.25%) | 9 (5.49%) |
| AMA | 5 (5.95%) | 6 (7.5%) | 11 (6.71%) |
| PROM | 1 (1.19%) | 0 (0%) | 1 (0.61%) |
| DM | 3 (3.57%) | 5 (6.25%) | 8 (4.88%) |
| Other | 3 (3.57%) | 1 (1.25%) | 4 (2.44%) |
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