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ORIGINAL RESEARCH |
From the Section of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Medical College of Wisconsin, Milwaukee, Wisconsin.
Address reprint requests to: Thomas R. Wigton, MD Medical College of Wisconsin Department of Obstetrics and Gynecology 9200 West Wisconsin Avenue Milwaukee, WI 53226 E-mail: twigton{at}mcw.edu
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Abstract |
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Methods: Women with Bishop scores less than 5 were assigned randomly to either extra-amniotic saline infusion (n = 26) or intracervical dinoprostone gel (n = 26) for preinduction cervical ripening. A sample size of 50 would have 80% power to detect a 10-hour difference in the mean time from start of cervical ripening to delivery for the two methods of intervention, with a type I error of .05.
Results: The study populations were similar in age, gestational age, and initial Bishop score. They differed in parity, with 22 nulliparas in the extra-amniotic saline infusion group versus 13 in the dinoprostone gel group (relative risk [RR] 1.69, 95% confidence interval [CI] 1.11, 2.57). The number of women achieving a favorable Bishop score at 6 hours was greater with extra-amniotic saline infusion (n = 20) than dinoprostone gel (n = 9) (RR 2.14, 95% CI 1.22, 3.75). Mean time from start of ripening to delivery was 25.9 hours with extra-amniotic saline infusion and 30.2 hours with dinoprostone gel (P = .25). Birth weight, Apgar scores, umbilical artery pH, and infectious morbidity were similar between groups.
Conclusion: More women achieved a favorable Bishop score at 6 and 12 hours after the start of cervical ripening with extra-amniotic saline infusion compared with dinoprostone gel. Saline infusion is as safe as dinoprostone gel for preinduction cervical ripening.
Labor induction often is indicated for maternal or fetal pregnancy complications, sometimes before the cervix has become favorable. Techniques to ripen the cervix artificially before labor induction shorten the course of labor and improve the chances of a successful vaginal delivery.1 Methods to ripen the cervix include intracervical balloon catheters and systemic and local prostaglandins. Among prostaglandin preparations, there are only two standardized, commercially available products in the United States for cervical ripening. One of these is a prepackaged dose of 0.5 mg of dinoprostone in 2.5 mL of a viscous gel, designed to be delivered intracervically (Prepidil Gel; Pharmacia & Upjohn, Kalamazoo, MI). Multicenter trials in the United States and Canada have confirmed the safety and efficacy of this agent.2,3
Balloon catheters have been used since the 1800s, but fell out of favor because of evidence that they increased the incidence of infection; however, recently balloon catheters have been shown to be safe and effective with proper aseptic technique.4 The addition of extra-amniotic saline infusion with a Foley catheter has been less extensively studied. Initial studies showed it to be more effective than intravaginal prostaglandins, with minimal side effects.5,6
The purpose of this study was to compare the efficacy and safety of extra-amniotic saline infusion with intracervical dinoprostone gel for preinduction cervical ripening.
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Materials and Methods |
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Assessment of gestational age was made on the basis of the last normal menstrual period, early reference examination, and ultrasound when available. Cervical status was ascertained on admission by the resident, attending physician, or certified nurse midwife. Unfavorable status was defined as a Bishop score less than 5.
Upon admission, eligible patients were asked about study entry. Randomization was done using a random numbers table, with randomization blocks providing a 1:1 ratio, balancing with every tenth patient. Assignments were inserted into consecutively numbered opaque envelopes, blinded to the investigators.
Subjects assigned to dinoprostone gel underwent a sterile speculum examination, and their cervices were swabbed with providone-iodine. Dinoprostone gel, warmed to room temperature (59–86 F) just before administration, was injected into the endocervical canal under direct visualization. Subjects remained supine for 15–30 minutes after administration. External fetal heart rate monitoring and tocodynometry were performed for at least 1 hour after placement of gel, and then for at least 20 minutes each hour. Six hours after the initial dose of dinoprostone gel, the cervix was reevaluated. If the Bishop score was less than 5, a second dose was placed. If the Bishop score was at least 5, induction of labor was initiated by amniotomy or infusion of oxytocin, at the discretion of the attending physician. Six hours after the second dose of gel (if required), the cervix was assessed for Bishop score and induction was initiated. Labor was otherwise managed according to the attending physician’s preference.
Women assigned to extra-amniotic saline infusion had sterile speculum examinations, their cervices prepared with betadine, and 26-gauge Foley catheters with 30-mL balloons inserted beyond the internal cervical os under direct visualization. Balloons were inflated with 30 mL of sterile water, and normal saline was infused through the catheter at 1 mL/minute with an infusion pump. The cervix was assessed for Bishop score after 6 hours or when the catheter was expelled. If the Bishop score remained less than 5, the infusion was continued for 6 more hours or until the catheter was expelled, whichever occurred first. If the Bishop score was at least 5, induction was initiated. In either group, for cases that failed to ripen, the second method chosen for cervical ripening was attending physician’s discretion. No patient was eligible for extra-amniotic saline infusion off protocol.
Cervical ripening failure was defined as failure to achieve a Bishop score of at least 5 at 12 hours. Intra-amniotic infection was defined as an oral temperature greater than 38 C (100.4 F) with uterine tenderness (with or without fetal tachycardia), without any other localizing signs of infection. Postpartum endomyometritis was defined as an oral temperature greater than 38C (100.4F) with uterine tenderness, without any other localizing signs of infection.
The major outcome variable was the time from start of cervical ripening to delivery. Other variables were the number of subjects with a favorable Bishop score, mode of delivery, and incidence of intra-amniotic infection or postpartum endomyometritis.
A power analysis found that to detect a 10-hour difference in mean time from start of cervical ripening to delivery for the two methods, required a sample size of 50. A pooled standard deviation of 12.41 hours, derived from other prostaglandin studies, was used to estimate the standard deviation for cervical ripening to delivery time for both groups. These calculations were based on a type I error of .05 and a power of 0.80. Relative risk (RR) with 95% confidence interval (CI), Student t test, and Fisher exact test were used when appropriate.
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Results |
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Indications for induction included hypertension (eight in the extra-amniotic infusion group, three in the dinoprostone gel group), post dates (four and five), fetal growth restriction (four and four), oligohydramnios (four and two), diabetes mellitus (zero and four), and unspecified (six and eight).
Seven participants’ courses did not follow the study protocol. One woman assigned to gel received two doses and was discharged home undelivered after 12 hours of oxytocin. This individual was included in the Bishop score analysis but not in the time from ripening to delivery. Another woman in the gel group had a fetus with breech presentation after the first dose was administered. She received oxytocin immediately after an external version. A subject in the extra-amniotic saline infusion group had a cervix with a very anterior position and the Foley catheter could not be placed. She received a 10-mg dinoprostone pessary (Cervidil; Forest Pharmaceuticals, St. Louis, MO). Four participants, three of whom were nulliparous, were enrolled despite having an initial Bishop score of 5. All patients were analyzed in the appropriate groups, consistent with an intent-to-treat analysis.
Outcome data are presented in Table 1
. At 6 hours, 14 women assigned to extra-amniotic saline and eight assigned to dinoprostone gel achieved Bishop scores of 5 to 7. Six in the extra-amniotic saline group and one in the gel group achieved scores of at least 8 at 6 hours. Six women (23%) required 12 hours of saline infusion and 16 (64%) required two doses of gel. At 12 hours, three (12%) in the extra-amniotic saline infusion group failed to achieve Bishop scores of 5 compared with 14 (56%) in the gel group (RR 2.01, CI 1.26, 3.20).
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). At 6 hours, ten of 22 women assigned to extra-amniotic saline and three of 13 assigned to dinoprostone gel achieved Bishop scores of 5 to 7. Six (27%) in the extra-amniotic saline infusion group and none in the gel group achieved scores of 8 or more at 6 hours. At 12 hours, three women (14%) in the extra-amniotic saline infusion group failed to achieve Bishop scores of 5, compared with eight (62%) in the gel group (RR 2.25, CI 1.11, 4.56).
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Discussion |
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We did not find a statistically significant difference in the time from the start of cervical ripening to delivery between the two groups. Our average time of 25.9 hours for extra-amniotic saline infusion is similar to that found by Sherman et al7 (21.2 hours). However, they excluded patients who delivered by cesarean from this calculation, which we did not. Vengalil et al8 reported a mean time from start of ripening to delivery of 16 hours, with extra-amniotic saline infusion plus oxytocin. In nulliparas in our study, the time to delivery was shorter by 8 hours in the extra-amniotic saline infusion group compared with the gel group. Forty subjects in each group were needed to achieve statistical significance for an 8-hour difference; therefore, our finding has limited statistical power. In patients requiring rapid induction, because of deteriorating maternal condition, such as severe preeclampsia, this 8-hour difference might be clinically relevant.
Technical difficulties occurred with only one participant; because of a cervix positioned very anteriorly the Foley catheter could not be placed. No side effects were reported from either group at the time of insertion, which is similar to findings in other studies. Schreyer et al5 reported mild bleeding (6%) shortly after catheter insertion, and Sherman et al7 reported rupture of membranes at the time of catheter insertion (2%). As in other studies, infectious morbidity rate did not differ from that of controls (extra-amniotic saline, 15.4%; dinoprostone gel, 26.9%).5,6
Among the shortcomings of our study, it was not possible for the examiners to be blinded to the treatment group, which might have introduced bias in the Bishop score examinations. However, the main outcome variable, time from the start of ripening to delivery, was objective. Also, there were four subjects with favorable Bishop scores. More nulliparas were assigned to extra-amniotic saline infusion, which occurred unexpectedly, and we thought this would bias our results in favor of dinoprostone gel, which did not occur.
When compared with intracervical dinoprostone gel, extra-amniotic saline infusion achieved a greater number of favorable Bishop scores, and in nulliparous patients led to clinically important shorter time from start of ripening to delivery.
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Footnotes |
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Received April 1, 1998. Received in revised form July 10, 1998. Accepted July 30, 1998.
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References |
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2. Keirse MJNC. Prostaglandins in preinduction cervical ripening: Meta-analysis of worldwide clinical experience. J Reprod Med 1993;38:89–100.[Medline]
3. Bernstein EP. Therapeutic considerations for preinduction cervical ripening with intracervical prostaglandin E2 gel. J Reprod Med 1993;38:73–7.[Medline]
4. Manabe Y, Manabe R. Nelaton catheter versus laminaria for a safe and gradual cervical dilation. Contraception 1981;24:53–60.[Medline]
5. Schreyer P, Sherman DJ, Ariely S, Herman A, Caspi E. Ripening the highly unfavorable cervix with extra-amniotic saline instillation or vaginal prostaglandin E2 application. Obstet Gynecol 1989;73:938–42.[Medline]
6. Rouben D, Arias F. A randomized trial of extra-amniotic saline infusion plus intracervical Foley catheter balloon versus prostaglandin vaginal gel for ripening the cervix and inducing labor in E2 patients with unfavorable cervices. Obstet Gynecol 1993;82:290–4.
7. Sherman DJ, Frenkel E, Tovgin J, Arieli S, Caspi E, Bukovsky I. Ripening of the unfavorable cervix with extra-amniotic catheter balloon: Clinical experience and review. Obstet Gynecol Surv 1996; 51:621–7.[Medline]
8. Vengalil S, Guinn DA, Olabi N, Burd L, Owen J. A randomized trial of misoprostol and extra-amniotic saline infusion for cervical ripening and labor induction. Obstet Gynecol 1998;91:774–9.[Abstract]
This article has been cited by other articles:
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  K. A. Levey, A. P. MacKenzie, C. Stephenson, R. Bercik, E. Kuczynski, and E. F. Funai Increased Rates of Chorioamnionitis With Extra-Amniotic Saline Infusion Method of Labor Induction Obstet. Gynecol., April 1, 2004; 103(4): 724 - 728. [Abstract] [Full Text] [PDF]
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D. J. SHERMAN, E. FRENKEL, M. PANSKY, E. CASPI, I. BUKOVSKY, and R. LANGER Balloon Cervical Ripening With Extra-Amniotic Infusion of Saline or Prostaglandin E2: A Double-Blind, Randomized Controlled Study Obstet. Gynecol., March 1, 2001; 97(3): 375 - 380. [Abstract] [Full Text] [PDF]
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