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A Randomized Comparison of Transcervical Foley Catheter to Intravaginal Misoprostol for Preinduction Cervical Ripening

From the Department of Obstetrics and Gynecology, Christiana Care Health Services, Maternal-Fetal Medicine Division, Newark, Delaware.

Address reprint requests to: Anthony C. Sciscione, DO Department of Obstetrics and Gynecology Maternal Fetal Medicine Division Christiana Care Health Services 4755 Ogletown-Stanton Road Newark, DE 19718 E-mail: asciscione{at}christianacare.org

	Abstract

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Objective: To compare the efficacy of intravaginal misoprostol tablets with transcervical Foley catheter for preinduction cervical ripening.

Methods: Pregnant women who presented for induction of labor with unfavorable cervices (Bishop score less than 6) were assigned randomly to intravaginal misoprostol (50 µg tablet every 4 hours for a maximum of six doses) or 30-mL Foley catheter placed transcervically with maintenance of traction.

Results: Among 111 women, 53 were allocated to misoprostol and 58 to Foley bulb. Contractile abnormalities were more frequent in the misoprostol group (20.4%) than the Foley group (0%) (P < .001). No statistically significant differences were noted between groups in change in Bishop score, preinduction cervical ripening times, and total induction times. There were no statistically significant differences in mode of delivery or adverse neonatal outcomes. Uterine rupture occurred in one woman with two previous cesarean deliveries in the misoprostol group.

Conclusion: Intravaginal misoprostol and transcervical Foley catheter are equivalent for cervical ripening. Uterine contractile abnormalities and meconium passage are more common with misoprostol.

Women who require labor induction often present with unfavorable cervices, which can lead to a prolonged and difficult induction. Preinduction cervical ripening is often done to increase the likelihood of successful labor induction.^1–3 More than 15% of pregnant women have preinduction cervical ripening and labor induction,⁴ so there is keen interest in developing safer, more cost-effective, and more efficient means of preinduction ripening.

Embrey and Mollison⁵ first described using a transcervical Foley catheter for cervical ripening. Obed and Adewole⁶ documented its effectiveness by increasing Bishop scores in women with unripe cervices. Since then, two studies found transcervical Foley catheters as effective as various prostaglandin (PG) preparations for ripening.^7,8 In a larger, randomized trial, we found that the Foley catheter was more effective and more economical than PGE₂ gel (Prepidil; Upjohn, Kalamazoo, MI) for providing preinduction ripening.⁹

Misoprostol (Cytotec, Searle Pharmaceuticals, Chicago, IL) is a PGE₁ analog, which is indicated for prevention of gastric ulcers in patients taking nonsteroidal anti-inflammatory drugs. Margulies et al¹⁰ suggested that the drug might be effective for induction of labor, so there has been great interest in the safety and efficacy of misoprostol, especially compared with PGE₂ agents for preinduction ripening. Multiple studies documented clinical advantages and cost benefits of intravaginal misoprostol compared with PGE₂ preparations for cervical ripening and induction of labor.⁴ However, some reports found a high rate of uterine contractile abnormalities.^11,12

We report the findings of a trial in which we compared efficacy of misoprostol to transcervical Foley catheter for preinduction cervical ripening.

	Materials and Methods

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After approval from the institutional review board at Christiana Care Health Services, the study was conducted from July 1, 1997, to July 1, 1999. All deliveries were at the Christiana Hospital, which serves as the tertiary referral center for the State of Delaware. Women who were admitted to the Labor and Delivery Suite for labor induction and met criteria for entrance in the trial were invited to participate. Women referred from outside hospitals who met entrance criteria and were being delivered at Christiana hospital also were offered entry. Inclusion criteria included singleton gestations in vertex presentation at greater than 28 weeks’ gestation. Women were monitored for at least 1 hour and had reactive nonstress tests without decelerations, and fewer than six contractions per hour. Each woman had a Bishop score assigned by her attending physician or an obstetrics and gynecology resident. Most of the time the person who assigned Bishop scores was the person doing preinduction cervical ripening and subsequent cervical examinations. Bishop score less than 6 was necessary for entry.

Exclusion criteria included rupture of membranes, antepartum bleeding, active genital herpes infection, fetal death, placenta previa, previous induction or preinduction agent during the pregnancy, and known allergy to misoprostol. Women with histories of cesarean deliveries were not excluded.

During computer-generated random allocation, methods of preinduction cervical ripening were placed consecutively in opaque envelopes by a research nurse and sealed. After written consent was obtained, each woman was assigned to receive cervical ripening with a transcervical Foley catheter or misoprostol, by selection of the next consecutive envelope.

All women who presented for induction had routine admission laboratory studies, (complete blood count and a type and screen) an intravenous (IV) infusion started, and continuous fetal heart rate monitoring and contraction monitoring before randomization. Only IV oxytocin could be used for labor induction after completion of the protocol for preinduction cervical ripening. No uniform guidelines for oxytocin were enforced, but almost all physicians used our hospital’s policy for it; beginning at 1 mIU and increasing 1 mIU every 15 minutes. Women who had spontaneous labor during or after preinduction ripening did not receive oxytocin unless a labor abnormality was diagnosed. Artificial rupture of membranes was done as soon as clinically feasible in both groups.

After meeting entrance criteria, a 16F Foley catheter with a 30-mL balloon was inserted into the endocervical canal under direct visualization during a sterile speculum examination for women assigned to transcervical Foley catheters. Cleansing or sterilization of the vagina or cervix was not done; however, every effort was made to avoid contact with the vagina or ectocervix with the catheter. The catheter was advanced into the endocervical canal. Once past the internal os, 30 mL of sterile water was injected into the balloon. Traction was applied by taping the end of the catheter to the medial side of the woman’s knee or thigh. The catheter was checked for extrusion of the balloon from the cervix every 6 hours by cervical examination. If the balloon had not been extruded, the catheter was adjusted to continue gentle traction. Each subject had external fetal monitoring for reactive nonstress tests after Foley catheter placement. Then she was allowed to ambulate with intermittent fetal heart rate (FHR) assessment every 30 minutes. Continuous external fetal monitoring was done every 2 hours for a reactive nonstress test or until regular, strong contractions ensued. There was no predicted time limit for the Foley catheter to be extruded. Once the catheter was extruded from the cervix, IV oxytocin was begun.

The group assigned misoprostol had 50 µg of misoprostol (Cytotec, Searle Pharmaceuticals, Chicago, IL) placed intravaginally. Because 50-µg tablets were not available, a 100-µg tablet was cut in half by the pharmacist, using a pill cutter. A 50-µg half tablet was placed in the posterior fornix of the vagina every 4 hours for a maximum of six doses. Women in that group had continuous external fetal monitoring. Subsequent doses were held if labor ensued or if uterine tachysystole, nonreassuring FHR, or rupture of membranes occurred. Oxytocin was begun 4 hours after the last dose of misoprostol in women who did not have spontaneous labor (regular contractions with continued cervical change), but had Bishop scores over 5, or if women had received six doses of misoprostol.

Our intent was to evaluate the success of preinduction cervical ripening, so the primary outcome measure was change in Bishop score. For women in the Foley catheter group, that was defined as the difference between initial cervical examination and examination at the time of extrusion. In the misoprostol group, it was the difference between initial examination and Bishop score assigned with the last dose of misoprostol. To detect a change of at least 1 in the Bishop score and maintain 80% power, with an alpha error of 0.05, using a variance of 3.96 from our previous trial,⁹ 50 women were needed in each group. Despite needing fewer women to find a larger difference in Bishop score change, we felt that a difference of 1 was the least that would be clinically important.

Secondary outcome measures included length of time for preinduction cervical ripening (time from placement of preinduction method until extrusion of Foley catheter, or 1 hour after the last dose of misoprostol), total time for induction (time of placement of ripening agent until delivery), delivery route, uterine tachysystole (defined as six contractions in 10 minutes, in two consecutive 10-minute periods), side effects, subject comfort, and FHR disturbances. Uterine tachysystole or uterine hypertonus (contraction lasting longer than 3 minutes) with a nonreassuring FHR pattern was described as hyperstimulation syndrome. Also, women were asked to evaluate their discomfort on a scale from 0 to 10 on the first postpartum day, with zero being no discomfort and 10 as the most pain the woman had ever felt. Student t test, Mann Whitney U Test, Fisher exact test, and ² were used when appropriate to compare groups. Values are stated as means with standard deviation (SD) unless otherwise noted. P < .05 was considered statistically significant.

	Results

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One hundred fourteen women were entered. Three were excluded because of deviations from entry criteria: one received a Foley catheter and misoprostol, one received 100 µg intravaginal misoprostol, and one had a transverse lie when oxytocin was begun. That left 111 eligible subjects, 58 of whom were assigned to catheters and 53 to misoprostol. Indications for induction of labor are presented in Table 1. Groups were similar in maternal age, gestational age at inclusion, gravidity, nulliparity, and Bishop score at entry (Table 2).

Women assigned to misoprostol received a mean of 2 ± 1.2 doses before beginning oxytocin or spontaneous labor. Twenty-one subjects (39.6%) in the misoprostol group did not require oxytocin because of spontaneous labor after misoprostol administration. No Foley catheter needed to be replaced after initial insertion and no patients had spontaneous labor in that group. Maternal side effects were infrequent. The most frequent complaint in the Foley group was mild discomfort at insertion. However, the amount of discomfort was mild to moderate in both groups, with the misoprostol group at a median discomfort level of 5.0 and the Foley group at a mean discomfort level of 4.0 (P = .87). There was no difference in epidural analgesia between groups, with 84% of the Foley group and 93% of the misoprostol group receiving epidural analgesia.

There was no statistically significant difference in median Bishop score at the end of preinduction cervical ripening or change in Bishop score between groups (Table 3). There was no difference in preinduction cervical ripening time or total time from the beginning of preinduction cervical ripening to delivery (Table 3). Also there was no difference in number of vaginal deliveries or total deliveries within 24 hours in each group (Table 4). The mode of delivery and infant weights were not statistically different between the groups (Table 4). The number of cesarean deliveries for nonreassuring fetal testing was higher in the misoprostol group, but the difference was not statistically significant (12% versus 24%; P = .09). However, there was a statistically significant increase in meconium passage in the misoprostol group. Mode of delivery and Bishop score change, were not significantly different between nulliparous women and multiparous women between groups.

	Discussion

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We found that a pharmacologic method of cervical ripening, misoprostol, and a mechanical method, the Foley catheter, were similarly effective and timely. However, significantly higher rates of uterine tachysystole and meconium passage were found in the misoprostol group. There were two cases of uterine hyperstimulation syndrome in the misoprostol group, both of which required immediate cesarean delivery.

All pharmacologic methods of cervical ripening have been associated with uterine contractile abnormalities. Misoprostol is no exception.¹¹ The rate of uterine contractile abnormalities has varied between 7.1 and 36.7%.⁴ The Foley catheter has been associated with rare uterine contraction abnormalities.⁷ In our previous trial, we reported a rate of 11.8%,⁹ partially caused by our liberal definition of hyperstimulation (six contractions in 10 minutes), and the technique for placement of the Foley bulb in that trial. All cases of hyperstimulation in our previous report were transient and shortly after placement of the catheter, and did not produce FHR abnormalities. In the current study we used a smaller Foley catheter, abandoned the obturator to help place the catheter, and no longer permitted a tenaculum to hold the cervix. No cases of hyperstimulation (using a more strict definition) or FHR abnormalities were noted in the Foley catheter arm in this trial. We were able to place all Foley catheters without an obturator or a tenaculum without difficulty.

We believe that methods that quantitate frequency of contractions are important for documentation and communication, but have little clinical value. Uterine contractile abnormalities are common in laboring women and often attract little attention until they begin to adversely affect fetuses. We believe that the most compelling and clinically useful definition is a uterine contraction abnormality that causes a nonreassuring FHR, which has been called hyperstimulation syndrome.¹² In this trial and other reports, hyperstimulation syndrome was not associated with Foley catheter alone for ripening.⁷ In a recent review of the literature, the relative risk (RR) of hyperstimulation syndrome was 1.45 (95% confidence interval [CI] 1.04, 2.04) with misoprostol,¹⁴ which might decrease with lower dosages.⁴

In a report by Perry et al,¹⁵ a Foley catheter with dinoprostone gel was compared with 25 µg of intravaginal misoprostol every 4 hours, and there was significant reduction in time to vaginal delivery and significantly more women delivered within 24 hours in the Foley-dinoprostone group. Although not statistically significant, the Foley-dinoprostone group had a lower frequency of hyperstimulation syndrome (3% versus 11%; P = .091). There are several significant differences between our trial and the report by Perry et al. The first and most obvious is the addition of dinoprostone gel to the Foley catheter; second is the larger balloon used in their trial (50 mL versus 30 mL); last is the smaller dose of misoprostol (25 µg versus 50 µg). Whether time advantages in the Perry et al trial were caused by addition of dinoprostone gel, the larger balloon, the smaller dose of misoprostol, or all three, is unclear.

In a report by Abramovici et al,¹⁶ oral misoprostol at 50 µg every 4 hours to a maximum of 300 µg was compared with Foley catheter placement with concomitant IV oxytocin. In our trial we found no difference in multiparous or nulliparous delivery within 24 hours, but they found a significantly higher percentage of multiparous women who delivered within 24 hours and shorter induction times in the Foley catheter and oxytocin group. Unfortunately, they also found a very high rate of uterine hyperstimulation syndrome (13%) in the Foley and oxytocin group. However, there were no differences in rate of cesarean delivery or neonatal outcomes.

Intravaginal misoprostol dosages have ranged from 25-, 50-, or 100-µg tablets every 4–6 hours to maximum doses as high as 800 µg.⁴ The 50-µg dosing appears to be associated with a significantly higher incidence of vaginal delivery within 24 hours and shorter induction to delivery times, compared with the 25-µg dose.¹¹ The 50-µg dose was associated with a higher rate of uterine tachysystole (36.8% versus 17.4%; P = .003) compared with the 25-µg dose. However, there does not appear to be a difference in uterine hyperstimulation syndrome (7.3% in the 50-µg group versus 5.8% in the 25-µg group).¹¹ In the same analysis, there was no greater incidence of adverse neonatal outcomes, thus, the only advantage to using 25 µg appears to be a lower rate of uterine tachysystole. We chose to use a 50-µg dosing schedule because we believed it would provide the best efficacy and safety.

Based on our experience,¹³ we agreed with Wing⁴ that caution should be exercised when using misoprostol in women with previous uterine surgeries. Until more experience with misoprostol in these women is accrued, we have abandoned its use at our institution.

Despite the randomized design of this trial, there were limitations. It was not possible to mask physicians to type of ripening method. A strict protocol for ripening should have minimized potential bias. The intent of the trial was to determine the efficacy of preinduction cervical ripening between methods, so no standardized protocol was devised or required for oxytocin administration or intrapartum management. Women with previous cesarean deliveries were not admitted after our adverse event, so the Foley in women with previous cesarean deliveries was not adequately studied. We have not had adverse events in women with previous surgeries using the catheter. We currently offer cervical ripening with Foley catheter to women with previous cesarean deliveries.

This report highlights the ability of the transcervical Foley catheter to serve purely as a preinduction ripening agent, with women in this report requiring added oxytocin to begin induction. Misoprostol, however, acts as a ripening agent and an induction agent, with close to 40% of women entering labor without added oxytocin. Misoprostol’s dual role in induction offers the small advantage of less nursing time in preparation and delivery of oxytocin. However, the associated increase in meconium passage and contractile abnormalities, combined with lack of significant time benefit or decrease in the cesarean delivery rate, minimize that advantage.

	Footnotes

 
PII S0029-7844(00)01186-8

Received September 6, 2000. Received in revised form November 9, 2000. Accepted November 29, 2000.

	References

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13. Sciscione A, Nguyen L, Manley J, Shlossman P, Colmorgen G. Uterine rupture during preinduction cervical ripening with misoprostol in a patient with a previous cesarean delivery. Aust NZ J Obstet Gynaecol 1998;38:1–2.[Medline]

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16. Abramovici D, Goldwasser S, Mabie BC, Mercer BM, Goldwasser R, Sibai BM. A randomized comparison of oral misoprostol versus Foley catheter and oxytocin for induction of labor at term. Am J Obstet Gynecol 1999;181:1108–12.[Medline]

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