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Does Cervical Ripening at Term Using a High Volume Foley Catheter Result in a Lower Caesarean Section Rate Than a Low Volume Foley Catheter? A Systematic Review and Meta-Analysis
Department of Obstetrics and Gynecology, McMaster University, Hamilton ONDepartments of Radiology and Clinical Epidemiology and Biostatistics, McMaster University, Hamilton ON
Cervical ripening with a Foley catheter before induction of labour is a common obstetrical intervention. In this study we aimed to evaluate primarily the relationship between high or low volume Foley catheters used for cervical ripening and Caesarean section, and secondarily the relationship between Foley catheter volume, cervical ripeness, and time to delivery. We searched Medline and Embase from their inceptions with the assistance of an experienced librarian. All abstracts and complete articles were independently reviewed by two reviewers, according to predefined inclusion criteria. Six hundred forty-eight abstracts were identified, and 30 complete articles were read in full. Three articles with a total of 575 participating women met the inclusion criteria. The rate of Caesarean section with use of 80 mL Foley catheters was not significantly different from the rate using 30 mL Foley catheters (RR 0.82; 95% CI 0.48 to 1.41). A favourable cervix (which was defined heterogeneously) was more common with high volume catheters (RR 1.72; 95% CI 1.46 to 2.04), and failure to deliver in 24 hours was lower (RR 0.70; 95% CI 0.54 to 0.90). High volume Foley catheters improve the likelihood of a favourable cervix and chance of delivery in 24 hours more than low volume Foley catheters. As a more favourable cervix before induction of labour is associated with a lower rate of Caesarean section, a randomized controlled trial comparing high and low volume Foley catheters for cervical ripening using Caesarean section as the primary outcome is warranted.
Résumé
La maturation cervicale au moyen d’une sonde de Foley avant le déclenchement du travail constitue une intervention obstétricale courante. Dans le cadre de cette étude, nous avons en premier lieu cherché à évaluer la relation entre la césarienne et l’utilisation de sondes de Foley de volume élevé ou faible aux fins de la maturation cervicale, pour ensuite chercher à évaluer la relation entre le volume de la sonde de Foley, la maturité cervicale et le délai avant l’accouchement. Nous avons mené des recherches dans Medline et Embase pour la période allant de leur mise en œuvre jusqu’au 22 octobre 2013, avec l’aide d’un bibliothécaire expérimenté. Tous les résumés et les articles intégraux ont fait l’objet d’une analyse indépendante menée par deux analystes, conformément à des critères d’inclusion prédéfinis. Six cent quarante-huit résumés ont été identifiés et 30 articles intégraux ont été lus au complet. Trois de ces articles (comptant un nombre total de 575 participantes) ont satisfait aux critères d’inclusion. Aucune différence significative n’a été constatée entre le taux de césarienne associé à l’utilisation de sondes de Foley de 80 ml et celui qui était associé à l’utilisation de sondes de Foley de 30 ml (RR, 0,82; IC à 95 %, 0,48 - 1,41). La présence d’un col favorable (concept dont la définition était hétérogène) était plus courante dans le cas des sondes de volume élevé (RR, 1,72; IC à 95 %, 1,46 - 2,04), tandis que l’incapacité de procéder à l’accouchement dans les 24 heures était moindre (RR, 0,70; IC à 95 %, 0,54 - 0,90). Les sondes de Foley de volume élevé sont associées à une meilleure amélioration de la probabilité d’obtenir un col favorable et de procéder à l’accouchement dans les 24 heures que celle que permettent les sondes de Foley de faible volume. Puisque la présence d’un col plus favorable avant le déclenchement du travail est associée à un taux moindre de césarienne, la tenue d’un essai randomisé comparant l’utilisation de sondes de Foley de volume élevé à celle de sondes de faible volume aux fins de la maturation cervicale (en utilisant la césarienne à titre de critère d’évaluation principal) s’avère justifiée.
Induction of labour is a common obstetrical intervention, undertaken when the benefits of delivery outweigh the risks of continuing the pregnancy. One in four pregnant women (25.2%) have labour induced,
One of the major concerns with induction of labour is the increased risk of Caesarean section compared with spontaneous onset of labour in women of comparable gestational age. Of primiparous women undergoing induction of labour, 29.3% deliver by Caesarean section; this is double the rate of those with spontaneous onset of labour (14.2%).
Before spontaneous labour, the cervix undergoes a physiological change; it changes from being long, closed, and firm to being in a state of “ripeness,” in which it softens, dilates, and shortens. Induction of labour is significantly more likely to result in a vaginal delivery if an unripe cervix is ripened before oxytocin is begun, using either mechanical methods
In its 2013 Clinical Practice Guideline, the Society of Obstetricians and Gynaecologists of Canada recognizes use of Foley catheters as a valid method of cervical ripening.
use of a Foley catheter for cervical ripening has been found to have a better safety profile than prostaglandin E2, with decreased tachysystole with fetal heart rate changes (RR 0.19; 95% CI 0.08 to 0.43). The PROBAAT trial,
an RCT comparing 30 mL Foley catheters and prostaglandin E2 for induction of labour in women at term, demonstrated decreased admissions of offspring to a neonatal ward (equivalent to level 2 nursery) with Foley catheter use compared with prostaglandins (RR 0.60; 95% CI 0.43 to 0.83), and a trend towards a decreased rate of Caesarean section for fetal distress (RR 0.62; 95% CI 0.37 to 1.04). A meta-analysis undertaken by the authors of the PROBAAT trial demonstrated that use of Foley catheters was associated with a decreased risk of tachysystole with fetal heart rate changes (RR 0.44; 95% CI 0.21 to 0.91), a decreased risk of postpartum hemorrhage (RR 0.60; 95% CI 0.37 to 0.95), and a trend towards decreased rates of umbilical cord pH<7.10 (RR 0.70; 95% CI 0.42 to 1.16).
Additionally, Foley catheters have been associated with less pain than prostaglandins during cervical ripening (pain score>4/10, 36% vs. 63%, P<0.001; overall discomfort 26% vs. 58%; P=0.003),
Induction of labour in nulliparous women with an unfavourable cervix: a randomised controlled trial comparing double and single balloon catheters and PGE2 gel.
Compared with those who used prostaglandins, women who had insertion of a Foley catheter were more likely to say they would choose that method of cervical ripening again.
Induction of labour in nulliparous women with an unfavourable cervix: a randomised controlled trial comparing double and single balloon catheters and PGE2 gel.
Multiple protocols of Foley catheter use with varying volumes have been described, including volumes of 30, 50, 60, and 80 mL. It is unknown if use of a higher volume Foley catheter for cervical ripening increases the chance of a vaginal delivery. Higher volume Foley catheters, because of their larger size, may result in a higher Bishop score, predominantly through cervical dilatation, before induction of labour with oxytocin. The likelihood of vaginal delivery is correlated with a higher Bishop score at the time of induction
; hence, it is postulated that a higher volume Foley catheter used for cervical ripening will be associated with a higher rate of vaginal delivery.
The objective of this study was to assess the effects of a high volume Foley catheter compared with a low volume Foley catheter used for cervical ripening on the rate of Caesarean section in women undergoing induction of labour at term. In addition, we assessed the effect of the volume of the Foley catheter on maternal and neonatal outcomes.
METHODS
With the assistance of an experienced reference librarian, we searched Medline and Embase for randomized controlled trials published from the inception of the databases (1946 and 1974, respectively) to October 22, 2013, comparing low volume and high volume Foley catheters for cervical ripening prior to induction of labour. Key words and MeSH headings used are listed in the online eAppendix. We included only studies involving pregnant women at≥37 weeks’ gestational age with an unripe cervix (as defined by the authors). Low volume single Foley catheter was defined as inflated to≤30 mL, and high volume single Foley catheter was defined as≥60 mL. Any comparisons between studies using double catheters were excluded.
No language restrictions were used. Published abstracts from conferences were included in the search. Bibliographies of all included articles were reviewed by two authors to search for other articles. Two reviewers (A.B. and D.E.) independently read all abstracts and selected relevant articles to read in full according to the inclusion criteria. Both reviewers read all articles, and any discrepancies between the authors about articles to include were resolved by discussion, with a third author (S.M.) as adjudicator as needed.
Two reviewers independently extracted information from the selected articles using a data collection sheet designed for this meta-analysis. The data collected included time frame and location of study; inclusion and exclusion criteria of the study; brand of Foley catheters used; volume of Foley catheters used; whether the Foley catheter was made of latex; whether traction was applied to the catheter; whether cervical ripening was done in an inpatient or outpatient setting; labour management, including use of artificial rupture of the membranes; whether ambulation was allowed; whether there was oxytocin use and at what point; and time from Foley catheter insertion to induction of labour. Primary and secondary outcomes of the study, mode of analysis, and bias were assessed. Confounding factors were recorded, along with patient demographics and outcomes. These data were then transferred to a spreadsheet and examined for discrepancies. Conflicting data were re-examined and resolved, with a third author (S.M.) available as adjudicator if needed. Two reviewers independently assessed methodological quality using the Cochrane collaboration’s tool for assessing risk of bias in randomized trials.
Disagreement was resolved by discussion or with a third author if needed.
The data were entered into Review Manager software version 5.2 (Nordic Cochrane Centre, Copenhagen, Denmark). Meta-analysis was undertaken with a fixed effects model using the Review Manager software. Analysis was carried out according to intention to treat. The denominator for each outcome was calculated as the number of randomized participants minus those with missing data.
Analysis of studies that compared Foley catheter volumes of≥80 mL to catheter volumes of≤30 mL were compared separately from studies comparing Foley catheters with volumes≥60 mL and≤30 mL. A fixed effects model was used to assess heterogeneity. Heterogeneity was suspected if I2 was greater than 30%.
Reporting bias using funnel plots was planned for all outcomes reported in five or more studies.
The primary outcome was the rate of Caesarean section following use of a high volume Foley catheter for cervical ripening, compared with the rate following use of a low volume catheter.
Secondary outcomes included both measures of effectiveness and complications.
Measures of effectiveness were:
1.
cervical ripeness, as described by dilatation and/or Bishop score and/or author’s definition, and
2.
delivery within 24 hours.
Complications were chorioamnionitis, cervical lacerations, antepartum hemorrhage, postpartum hemorrhage, epidural rates, oxytocin use, malpresentation, umbilical cord prolapse, passage of meconium, umbilical cord blood gases, five-minute Apgar score, operative vaginal delivery, Caesarean section for failure to progress in labour, and Caesarean section for fetal distress.
RESULTS
Using the search strategy described, a total of 648 potential individual abstracts were identified (Figure 1). After the abstracts were read, 30 were selected for full review of the journal article and were read in their entirety, including the reference lists and bibliographies. No further articles were identified in the reference lists and bibliographies. Twenty-seven articles were then excluded, most commonly because they did not compare Foley catheters of two different volumes. Three articles ultimately met the inclusion criteria.
In this study all patients were inpatients, and received oxytocin started ½ hour after the placement of the Foleys. There was no mention of standardization of management of the membranes.
Singleton pregnancies
Cephalic presentation
Undergoing induction of labour, with initial Bishop score of<5
Maternal age of those with high volume Foleys vs. low volume Foleys: 29.4±6.5 vs. 31.4±6.9, P=0.03
76% of women were nulliparous in both groups (P>0.99)
Prostaglandin use before Foley placement in those with high volume Foleys vs. low volume Foleys: 27% vs. 46%, P=0.87
80 mL Foley no. 26, Malaysia (as per personal communication with author)
30 mL no. 26, Malaysia
90
90
All patients were induced as inpatients with a 500 g weight applying traction to the cervix. Oxytocin was started 6 hours after the Foley was placed. There is no mention of standardized management of the membranes.
Singleton pregnancies
Cephalic presentation
Undergoing induction of labour with an initial Bishop score≤5.
Maternal age of those with high volume Foleys vs. low volume Foleys: 24.3±5.0 vs. 24.7±4.0, P=0.74
Maximum parity of 2
Parity of those with high volume Foleys vs. low volume Foleys: 0.41±0.49 vs. 0.31±0.46, P=0.23.
Gestational age described as “term” Singleton pregnancies
Kaplan Medical Center, Rehovot, Israel
80 mL Foley catheter (no mention of brand, attempt has been made to contact author)
30 mL Foley
100
103
After placement, the Foley was taped with gentle traction to the thigh, and removed after 12 hours or when abnormal fetal monitoring was noted. Patents were then started on oxytocin, or their membranes were ruptured if they were already contacting 3 times in 10 minutes.
Cephalic presentation
Undergoing induction of labour with an initial Bishop score of<4
Maternal age of nulliparas with high volume Foleys vs. low volume Foleys: 26.8±4.3 vs. 25.5±4.3, P=0.15
Maternal age of multiparas with high volume Foleys vs. low volume Foleys: 28.3±4.9 vs. 30.0±5.6, P=0.51
Nulliparas with high volume Foleys vs. nulliparas with low volume Foleys: 49.0% vs. 50.5%, P=0.83
used envelopes marked A,B, and C without clearly describing how the sequence was generated, suggesting a high risk of bias. The allocation was well concealed in two of the studies,
had a low risk of attrition bias, with either no missing outcomes or missing outcomes balanced across groups. Two of the studies had a high risk of reporting bias, one due to poorly specified outcomes
Forest plots from the meta-analysis are shown in Figure 2, and summaries of all findings are shown in Table 3. There was no difference in the primary outcome of Caesarean section rate (RR 0.94; 95% CI 0.65 to 1.38),
when 60 mL and 80 mL Foley catheters were included in the high volume group. When only the studies with the 80 mL Foley catheters were included, there was still no difference in the rate of Caesarean section (RR 0.82; 95% CI 0.48 to 1.41),
High volume Foley catheters resulted in a significant improvement in the Bishop score before induction of labour compared with low volume catheters. Because of heterogeneous reporting of cervical ripeness, only two of the studies
could be included in the meta-analysis using the authors’ definition of a favourable or ripe cervix (a Bishop score of 9 and cervical dilation of≥3 cm, respectively) (RR 1.72; 95% CI 1.46 to 2.04).
High volume Foley catheters resulted in a significantly reduced likelihood of failure to deliver in 24 hours (RR 0.70; 95% CI 0.54 to 0.90),
There was a significant difference between high and low volume Foley catheters in the rate of Caesarean section for failure to progress in labour (3% vs. 9.7%, P=0.047),
To our knowledge, this is the first meta-analysis to examine the relationship between use of high volume and low volume Foley catheters for cervical ripening and mode of delivery.
Three studies with a total of 575 women met the inclusion criteria for our study. The quality of the included studies varied, and there is a need for more high quality studies. None of the studies we reviewed had mode of delivery as a primary outcome, nor were they statistically powered to detect this outcome. We found no significant decrease in rates of Caesarean section according to catheter volume.
There was a significant increase in the ripeness of the cervix with use of a high volume Foley catheter. Previous studies have shown a positive relationship between Bishop score at initiation of induction of labour and the likelihood of vaginal delivery.
Nulliparous low risk women who have labour induced for premature rupture of the membranes have a reduction in the risk of Caesarean section for every one-point increase in the Bishop score (OR 0.78; 95% CI 0.68 to 0.88).
found an increase in the risk of Caesarean section when induction of labour began with a Bishop score of≤5 (OR 2.32; 95% CI 1.66 to 3.25), and a systematic review and meta-analysis by Kolkman et al.
found that a Bishop score of<8 has a positive predictive value of 21% for requiring Caesarean section (95% CI 20% to 23%) and a negative predictive value of 96% (95% CI 95% to 98%), meaning that 96% of women with a Bishop score of≥8 undergoing induction of labour have a vaginal delivery.
We found that use of high volume Foley catheters, including 60 mL and 80 mL catheters, was associated with a statistically significant reduction in failure to deliver in 24 hours. There may be a graded relationship between higher Foley catheter volume and failure to deliver in 24 hours.
examined indications for Caesarean section, and found fewer Caesarean sections were performed for failure to progress in labour in the 80 mL group than the 30 mL group (3.0% vs. 9.9%, P=0.047). This is important, because the PROBAAT trial,
which compared the effectiveness of a 30 mL balloon catheter with prostaglandin E2 gel for ripening the cervix, showed that the major reason for Caesarean section in the Foley catheter group was failure to progress in labour, with a Caesarean section rate similar to that in women who used prostaglandin E2.
described a trend towards an increased number of Caesarean sections in the high volume Foley catheter group being performed for non-reassuring fetal heart rate tracings (6% vs. 1%, P=0.09). Further studies are warranted.
In the studies we reviewed, there was heterogeneity in the management of labour and various definitions of a “ripe” cervix. The participants in all three studies included both nulliparous and multiparous women, which increased the generalizability of our findings; however, including both groups of women would have affected the usefulness of Caesarean section as an outcome. Multiparous women have a 95% chance of delivering vaginally if they have labour induced, whereas nulliparous women who have labour induced have only a 68% chance of vaginal delivery.
evaluated multiparous and nulliparous women separately and found that the shorter time to delivery and decreased need for oxytocin augmentation in women who used the high volume Foley catheter rather than the low volume was due to the greater effect in nulliparous women. This appeared to be an important point to take into account when designing future studies.
This study’s strengths include a thorough assessment of the literature, using the assistance of an experienced librarian using MeSH and key word terms. Bias was limited by the lack of language limitations. The limitations include the small number of studies available for assessment, the small number of participants in each study, and the inconsistencies in both protocols and the reporting outcomes.
CONCLUSION
Use of high volume Foley catheters for cervical ripening was not associated with a statistically significant decrease in the rate of Caesarean section, although the numbers in our study were relatively small. There was a slight shift in favour of using high volume Foley catheters when the effects of 80 mL Foley catheters were compared with those of 30 mL catheters. High volume Foley catheters increased cervical ripeness and the probability of delivery within 24 hours more than low volume catheters.
Our findings suggest the need for a large RCT using Caesarean section as a primary outcome. It may be beneficial to consider multiparous and nulliparous women separately, as they have a different baseline risk of requiring Caesarean section.
REFERENCES
Better Outcomes Registry & Network (BORN) Ontario
Perinatal Health Report 2009–2010.
in: Waterloo Wellington and Hamilton Niagara Haldimand Brant—LHINs 3 & 4. BORN,
Ottawa ON2011
Induction of labour in nulliparous women with an unfavourable cervix: a randomised controlled trial comparing double and single balloon catheters and PGE2 gel.
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