Induction of labour in nulliparous women with an unfavourable cervix: a randomised controlled trial comparing double and single balloon catheters and PGE2 gel



This article is corrected by:

  1. Errata: Corrigendum Volume 118, Issue 4, 521, Article first published online: 10 February 2011

Dr CE Pennell, School of Women’s and Infants’ Health (M550), The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia. Email


Objective  To compare the efficacy and patient satisfaction of three methods of labour induction (double balloon catheters, single balloon catheters and prostaglandin gel) in term nulliparous women with unfavourable cervices.

Design  Randomised controlled trial.

Population  A total of 330 nulliparous women with unfavourable cervices induced at term.

Methods  Three cervical ripening study arms were used: double balloon catheter (107 women); 16F Foley catheter (110 women) and PGE2 gel (2 mg) (113 women).

Main outcome measures  Caesarean section, induction to delivery interval, adverse reactions and patient satisfaction.

Results  There was no difference in caesarean delivery rates between groups (double balloon 43%, single balloon 36%, PGE2 37%, = 0.567). The induction to delivery interval was longer in the double balloon group (median 24.5; 95% CI 23.7, 30.6 hours) than the single balloon (23.2; 20.8, 25.8 hours) or PGE2 (23.8; 21.7, 26.8 hours) (= 0.043). Uterine hyperstimulation occurred in 14% of the PGE2 group with none occurring with mechanical cervical ripening. Cord blood gases were worse in the PGE2 group: median arterial pH double balloon 7.26 (range 7.03–7.40); single balloon 7.26 (7.05–7.44); PGE2 7.25 (6.91–7.41) (= 0.050). Cervical ripening with the single balloon catheter was associated with significantly less pain (pain score ≥4: double balloon 55%, single balloon 36%, PGE2 63%, < 0.001).

Conclusions  Labour induction in nullipara with unfavourable cervices results in high caesarean delivery rates. Although all methods in this study had similar efficacy, the single balloon catheter offers the best combination of safety and patient comfort.


Induction of labour is a common procedure in obstetrics, occurring in up to 30% of pregnancies.1,2 The success of induction depends on the state of the cervix before commencement with the most favourable outcomes occurring in cervices which are soft and effaced.3 A cervix that is closed, firm and difficult to distend increases the likelihood of failed induction, longer duration of labour and caesarean section.4,5 Although many methods are used to ripen the cervix before induction is attempted, there is little consensus on the best method.2,6–9 Induction of labour is most challenging in nulliparous women,10 and the optimum technique for cervical ripening in this group is unknown.11

The method most commonly used to identify readiness for onset of labour is the modified Bishop score which includes quantitative measures of consistency and dilation of the cervix, and station and position of the presenting part.12 Originally developed to assess the likelihood of labour in multiparous women, it has since been applied to nulliparous women undergoing induction of labour.13 Fetal fibronectin (FFN) collected from the cervico-vaginal fluid is typically used to predict preterm birth in women with contractions; however, it has also been shown to correlate with the Bishop score.14,15 There is increasing evidence that positive FFN is an effective predictor of favourable outcomes with induction of labour,16,17 although its role in nulliparous women has not been established.18

Common cervical ripening methods include biochemical and mechanical agents. Synthetic prostaglandins such as prostaglandin E2 (PGE2) imitate normal physiological cervical ripening and increase the sensitivity of the uterine myometrium to oxytocin.3,7 While PGE2 reduces the likelihood of caesarean section compared with placebo, the fourfold increase in risk of uterine hyperstimulation with fetal heart changes is concerning.7

Mechanical ripening devices apply pressure on the internal os of the cervix, overstretching the lower uterine segment and indirectly increasing localised secretion of prostaglandin.6 These devices are easy to insert, relatively low cost, and have few adverse effects. Furthermore, studies have shown no increased risk of perinatal infections with the use of a single balloon (Foley) catheter for cervical ripening.19 A number of randomised controlled trials have investigated the efficacy of Foley catheters. While the risk of caesarean section is reduced when Foley catheters are compared with oxytocin, comparison with PGE2 is inconclusive.6 Furthermore, most studies included women with mixed parities and few studies focused on nulliparous women with unfavourable cervices.

The double balloon catheter has a cervicovaginal balloon in addition to the uterine balloon, allowing greater compression of the cervical os.20 Preliminary observational studies and two small randomised controlled trials demonstrated effective cervical ripening with low rates of caesarean section compared with PGE2.20–23 Conclusions from these studies are limited by the inclusion of both nulliparous and multiparous women and small samples sizes. Furthermore, no study has compared the double balloon with the single balloon Foley catheter for cervical ripening.

The present study was undertaken to compare the efficacy, safety and patient satisfaction of three methods of induction in nulliparous women with an unfavourable cervix: prostaglandin gel, a single balloon Foley catheter and a double balloon catheter.


Recruitment and randomisation

Women requiring induction of labour were recruited in the antenatal clinics of King Edward Memorial Hospital (KEMH) in Perth, Western Australia between July 2001 and December 2003. The hospital is the only tertiary obstetric hospital in the state and conducts over 5000 deliveries per year. The trial was approved by the institutional ethics committee.

Nulliparous women over 36 weeks’ gestation, with a singleton fetus in cephalic presentation, intact membranes and a modified Bishop score of 0–4 were eligible for inclusion. Exclusion criteria were age <16 years, previous uterine surgery, low-lying placenta, any active or purulent infection of the lower vaginal tract, or an abnormal pre-induction fetal heart rate (FHR) tracing.

Women were given information about the trial when the decision was made for induction of labour. Informed consent was obtained on admission to the delivery ward. Before randomisation, FFN swabs were collected by speculum examination on women without contraindications, low vaginal swabs were collected to exclude abnormal bacterial growth and Bishop Scores were confirmed to be between 0 and 4. To minimise variation, all initial pre-induction cervical assessment was conducted by one of two principal investigators (CEP or MJO).

Randomisation was conducted after stratification by FFN status (positive, negative or not performed). Each participant selected an opaque envelope from a selection of 12 envelopes. Blinding of participants or care providers was not possible.


Women recruited to the study were randomised to one of the following three cervical ripening methods:

Prostaglandin gel: PGE2 gel (2 mg, Prostin E2; Pfizer Australia, West Ryde, NSW, Australia) was placed into the posterior fornix of the vagina. This was repeated six hourly up to a maximum of three doses unless the Bishop score was greater than six or regular painful contractions <5 minutes apart had commenced. External electronic fetal heart rate monitoring (EFM) was conducted before and for a minimum of 60 minutes after each PGE2 insertion. Artificial rupture of the membranes was attempted and oxytocin infusion was commenced if labour did not commence after three doses.

Single balloon catheter: A 16F Foley catheter (Western Biomedical, Subiaco, WA, Australia) was inserted above the internal cervical os, and filled with 30 ml of sterile water. The catheter was strapped to the inner aspect of one leg on slight tension. The catheter was removed after 12 hours if spontaneous expulsion had not occurred. EFM was conducted before and for a minimum of 60 minutes after catheter insertion. Artificial rupture of the membranes and oxytocin infusion was commenced if labour did not commence after removal or expulsion of the catheter.

Double balloon catheter: A double balloon catheter (Atad Ripener Device; Gyne-Medical Technologies Pty Ltd, Melbourne, Vic, Australia) was inserted through the cervix and the balloons either side of the cervix were inflated with 80 ml of water, similar to previous studies 21–23 and in accordance the recommendations from the manufacturer. The catheter was taped to the inner thigh (without tension) for patient comfort as the two balloons place pressure on the cervical os without tension on the catheter. Each catheter insertion was supervised by a trial investigator. Management of women with the double balloon catheter was identical to that of the single balloon catheter.

Management of established labour

Labour was managed by the attending obstetricians and midwives. Assessment of labour progress was conducted using existing protocols in the unit. In women with spontaneous onset of labour, amniotomy was performed after cervical dilatation of 3 cm. Oxytocin augmentation was commenced if there was inadequate progress 4 hours after membrane rupture.8 The oxytocin infusion was escalated as required to maintain regular moderate to strong contractions. Analgesia was administered at maternal request according to unit protocols.

Continuous EFM was used throughout established labour. All cardiotocographs were reviewed after delivery by a principal investigator who was blinded to group allocation. Hyperstimulation of the uterus was defined as either the occurrence of five or more contractions in 10 minutes for two consecutive 10-minute periods or a contraction lasting at least 2 minutes, with or without changes in FHR patterns.2 FHR traces were considered non-reassuring if there was persistent reduced baseline variability, late decelerations and/or complicated variable decelerations. Fetal scalp blood acid–base sampling was undertaken by the attending obstetrician if indicated for non-reassuring FHR patterns.

There is no standard definition for what constitutes a failed induction of labour.24 In this study, we have defined a failed induction of labour as: inability to rupture the membranes after three doses of PGE2 or 12 hours of mechanical ripening or a cervical dilatation of <4 cm after 8 hours of strong contractions. Indications for caesarean section were failed induction of labour, failure to progress in established labour or non-reassuring fetal status (based on EFM patterns) as assessed by the attending obstetrician.

Adverse reactions were assessed during cervical ripening, labour and the puerperium including: inability to tolerate the mechanical ripening device, inability to void during cervical ripening, uterine hyperstimulation, abruptio placenta and infections or readmission during the puerperium.

Data collection

Trained research midwives, who were blind to treatment allocation, collected labour and delivery data and administered patient satisfaction questionnaires 24–48 hours after delivery. Women completed visual analogue scales (VAS, 0–10) to assess: (i) overall satisfaction with induction of labour, (ii) pain on insertion of the ripening device or gel and (iii) pain during cervical ripening.

Statistical methods

The primary outcome for this study was the rate of caesarean section. Secondary outcomes included: indications for caesarean section (non-reassuring fetal status or failed induction), induction to delivery interval, adverse reactions to ripening agents and patient satisfaction.

Outcome data are presented as percentages or medians with inter-quartile ranges. The primary endpoint was analysed on an intention to treat basis using the Chi-square test at the 0.05 level of significance. Sample sizes of 110 women per group were sufficient to attain 80% power to detect a 50% reduction in the caesarean section rate from 30% to 15%. A post hoc evaluation of the primary outcome was conducted out using logistic regression analysis that modelled the probability of caesarean section, given mode of induction and other candidate covariates including Bishop Score, FFN and reason for caesarean. Continuous data was analysed using the Kruskal–Wallis non-parametric analysis of variance. Time to delivery was analysed using Kaplan–Meier survival plots and Log Rank Tests with censoring at the time of caesarean section. SPSS version 15.0 (SPSS Inc, Chicago, IL, USA) was used for all statistical analysis.



Over the study period 524 women were eligible for inclusion into the study. Of the 390 women invited to participate, 60 declined to participate (Figure 1). There were no withdrawals or losses to follow up and complete data were available for all 330 women randomised to the trial.

Figure 1.

 Recruitment and flow of patients with cervical ripening during study.

There were 11 protocol violations (Figure 1). One woman in the PGE2 group had a Foley catheter inserted after two doses of gel. Six women in the single balloon group received PGE2 gel after either insertion difficulties (= 2) or unsuccessful cervical ripening (= 4). Three of these women proceeded to assisted vaginal deliveries and three to caesarean section. Four women in the double balloon group received PGE2 gel after either removal for maternal side-effects (= 2) or unsuccessful cervical ripening (= 2). Two of these women had spontaneous vaginal deliveries and two caesarean sections.

Pre-induction results

All groups were similar at baseline (Table 1). Only 5% of the women were induced before 37 weeks of gestation. Indications for induction of labour were not different between groups, with the majority of women undergoing induction of labour for prolonged pregnancy or hypertension. There were no differences in pre-induction cervical assessment with 58% having negative FFN. Bishop score distribution was similar both between groups and also between the two primary investigators (= 0.213).

Table 1.   Patient demographic data
Double balloon (n = 107)Single balloon (n = 110)PGE2 (n = 113)
  1. Values are n (%) unless indicated otherwise.

  2. *Median (range). There were no significant differences between groups (> 0.05).

Age*27 (16–40)26 (16–44)27 (16–42)
178 (73)72 (66)71 (63)
217 (16)24 (22)29 (26)
3+12 (11)13 (12)12 (11)
Gestational age*40 (36–42)40 (36–42)40 (36–42)
GA <37 weeks4 (4)5 (5)4 (4)
Indication for induction (%)
Postdates47 (44)38 (35)41 (36)
Hypertensive disease24 (22)33 (30)29 (26)
Diabetes mellitus10 (9)5 (5)5 (4)
Other maternal indication10 (9)11 (10)20 (18)
Intrauterine growth restriction8 (7)11 (10)7 (6)
Abnormal fetal welfare test4 (4)9 (8)4 (4)
Other fetal indication4 (4)3 (3)7 (6)
Fetal fibronectin
Negative64 (60)62 (56)65 (58)
Positive12 (11)14 (13)15 (13)
Not performed31 (29)34 (31)33 (29)
Modified Bishop score
0–241 (38)40 (37)29 (26)
3–466 (62)69 (63)84 (74)

There was no relationship between FFN and initial Bishop Score (= 0.622) or duration of induction or labour (= 0.435 and 0.196 respectively). In the group of women who received PGE2 gel, the mean number of prostaglandin doses was 1.8. The total dosage of PGE2 gel was not associated with either pre-induction Bishop score (= 0.331) or FFN (= 0.442). There were no differences between groups in pre-induction vaginal swab results either for abnormal swabs or the pattern of bacterial colonisation.


Overall 38% of women required caesarean section. There was no difference in caesarean section rates between any of the groups [double balloon 43%, RR (95% CI) 1.16 (0.82–1.39); single balloon 36%, 0.98 (0.67–1.35); PGE2 37%, RR 1.00; = 0.567; Table 2].

Table 2.   Delivery outcomes
Double balloon (n = 107)Single balloon (n = 110)PGE2 (n = 113) 
  1. Values are n (%) unless indicated otherwise.

  2. FHR, fetal heart rate; PPH, postpartum haemorrhage.

  3. *Median (95% CI) estimated from Kaplan–Meier survival analysis, censored for caesarean section.

  4. **Median (interquartile range).

Mode of delivery
Spontaneous vaginal delivery38 (36)45 (41)43 (38)0.715
Assisted vaginal delivery23 (22)25 (23)28 (25)0.845
Caesarean section46 (43)40 (36)42 (37)0.567
Indication for caesarean section   0.168
Non-reassuring FHR pattern15 (33)14 (35)20 (47) 
Failure to progress21 (46)14 (35)17 (41) 
Failed induction of labour10 (22)12 (30)5 (12) 
Indication for assisted vaginal delivery   0.113
Non-reassuring FHR pattern7 (30)12 (48)15 (54) 
Other16 (70)13 (52)12 (46) 
Fetal scalp blood sampling17 (16)13 (12)28 (25)0.035
Induction to delivery time* (hours)24.5 (23.7–30.6)23.2 (20.8–25.8)23.8 (21.7–6.8)0.043
Time to active labour* (hours)16.1 (15.1–17.1)14.3 (11.9–16.3)14.5 (13.4–8.3)0.014
Length of labour* (hours)9.8 (9.3–13.0)10.3 (8.9–11.2)9.0 (7.42–11.0)0.152
Vaginal Delivery <24 hours 40 (37)53 (48)49 (43)0.274
Epidural89 (83)90 (81)92 (81)0.951
Temperature in labour18 (17)19 (17)20 (18)0.999
Antibiotics in labour26 (24)26 (24)19 (17)0.316
Blood loss at delivery
Volume (ml)**450 (300–600)400 (200–550)400 (300–600)0.141
PPH >500 ml41 (39)43 (39)47 (42)0.845
PPH >1000 ml5 (5)5 (5)12 (11)0.143

More caesarean sections were performed for non-reassuring FHR patterns (47%) and fewer for failed induction (12%) in the PGE2 group compared with mechanical groups, although this did not reach statistical significance. Similarly, non-reassuring FHR tracing was a more frequent indication for assisted vaginal delivery in the PGE2 group.

Allocated group was not associated with caesarean section in the multivariate analysis. Significant predictors of caesarean section were older maternal age (compared with age 20–25 years OR, 95% CI: age 30–35 years 2.14, 1.06–4.31; age ≥35 years 3.83, 1.63–8.97), higher station of the presenting part at initial vaginal assessment (0.57, 0.35–0.91) and no cervical dilatation at initial vaginal assessment (0.59, 0.36–0.97).

There were no differences in spontaneous vaginal delivery, assisted vaginal delivery or length of active labour between the three groups (Figure 2, Table 2). The double balloon group had a longer induction to delivery interval and this was because of a longer time to commencement of active labour (= 0.014). There were no differences in analgesia use, maternal temperature during labour (>37.5°C), administration of antibiotics or postpartum blood loss.

Figure 2.

 Time from induction to delivery. Proportion of women remaining undelivered estimated with Kaplan–Meier survival curves. The double balloon group had a longer induction to delivery interval (median, 95% CI 24.5, 23.7–30.6 hours) than the PGE2 (23.8 21.7–26.8 hours) or single balloon (23.2, 20.8–25.8 hours, = 0.043). This was because of a longer time to commencement of active labour (see Table 2) in the double balloon group (= 0.014).

The PGE2 group required significantly more fetal scalp blood samples for non-reassuring FHR tracing than other groups (Table 2). More women (8%) in the PGE2 group were delivered by caesarean section for abnormal fetal scalp results compared to single and double balloon groups (3% and 2% respectively).

Neonatal outcomes differed between groups (Table 3). Cord blood gases were worse in the PGE2 group than the other two groups with lower arterial and venous cord pH and PO2 values and higher PCO2 values in the PGE2 group. Although the shift in blood gas distributions towards acidaemia was statistically significant, of greater clinical significance is the proportion of neonates with cord arterial pH values <7.10: single balloon group (= 3, 2.7%), double balloon (= 7, 6.5%) and PGE2 groups (= 8, 7.1%). Moreover, four of the five cases of severe neonatal acidaemia (pH <7.0 and/or base excess <−12 mmol/l) occurred in the PGE2 arm of the study with one neonate with a base excess <−12 mmol/l in the double balloon arm of the study and no cases of severe acidosis after cervical ripening with a Foley catheter. Twenty five percent of neonates required admission to the neonatal special care unit with no significant difference between groups.

Table 3.   Neonatal outcomes
Double balloon (n = 107)Single balloon (n = 110)PGE2 (n = 113) 
  1. Values are n (%) or median (range).

  2. *Reasons for nursery admissions (= 0.544): neonatal conditions include birth trauma, asphyxia, respiratory, unstable temperature, jaundice requiring phototherapy; fetal conditions include growth restriction, congenital abnormalities; mother unable to care for infant because of admission to the Adult Special Care Unit.

Birth weight (g)3540 (2070 to 5305)3405 (1620 to 4785)3440 (2000 to 4830)0.035
Apgar < 4 at 1 min2 (2)0 (0)1 (1)0.322
Apgar <7 at 5 min0 (0)2 (2)3 (3)0.378
Arterial blood gases
pH7.26 (7.03 to 7.40)7.26 (7.05 to 7.44)7.25 (6.91 to 7.41)0.050
pO215.4 (2.6 to 92.7)17.5 (2.7 to 59.1)14.7 (1.30 to 66.2)0.003
pCO255.3 (10.4 to 96.5)53.2 (20.6 to 90.9)57.8 (26.3 to 84.5)0.003
Base excess (mmol/l)−4.0 (−12.8 to 0.7)−4.4 (−12.0 to 0.9)−4.0 (−15.1 to 0.7)0.796
Nursery admissions*21 (20)29 (27)33 (29)0.245
Neonatal conditions7 (33)15 (54)15 (47) 
Fetal or congenital conditions6 (29)6 (21)5 (16) 
Mather unable to care for infant8 (38)7 (25)12 (38) 

There were significantly more adverse reactions in the PGE2 group (< 0.001) than in the other groups (Table 4). Fourteen percent (= 16) of the PGE2 group experienced uterine hyperstimulation: non-reassuring FHR patterns associated with uterine hyperstimulation occurred in five cases and one caesarean section was required. The majority of episodes (75%) of uterine hyperstimulation occurred with the first dose of PGE2, with 25% occurring with the second dose and none with the third dose which was required in 20% of the women in the PGE2 group. Of the 16 cases of uterine hyperstimulation, ten occurred within the first hour and one within the second hour after PGE2 administration. The remaining five cases occurred between 4 and 6 hours after PGE2 administration. One emergency caesarean section was performed for placental abruption in the PGE2 group. Five women experienced adverse reactions in the double balloon group with none in the single balloon group. Two women experienced pain with the double balloon catheter in situ, with one woman requesting removal of the catheter. Three women were unable to void, and one woman required an indwelling urinary catheter. There were no differences in postnatal outcomes between groups including length of stay (= 0.427).

Table 4.   Adverse reactions
Double balloon (n = 107)Single balloon (n = 110)PGE2 (n = 113) 
  1. FHR, fetal heart rate.

  2. *≥5 uterine contractions in 10 minutes for two consecutive 10-minute periods within 6 hours of insertion of mechanical ripening device or within 6 hours of insertion of individual PGE2 doses.

  3. **Percentages reported for those re-presenting to hospital.

  4. ***Includes urinary tract infection, increased vaginal loss and infected perineum.

Any induction/intrapartum adverse event5 (5)0 (0)17 (15)<0.001
Ripening Device
Unable to void2 (2)0 (0)0 (0) 
Decreased balloon volume because of discomfort2 (2)0 (0)0 (0) 
Device removed because of discomfort1 (1)0 (0)0 (0) 
Uterine hyperstimulation*0 (0)0 (0)16 (14) 
Tachysystole and normal FHR pattern0 (0)0 (0)11 (9) 
Tachysystole and non-reassuring FHR pattern0 (0)0 (0)5 (4) 
Tachysystole and non-reassuring FHR pattern requiring delivery0 (0)0 (0)1 (1) 
Abruptio placenta0 (0)0 (0)1 (1) 
Re-presentation to hospital after discharge4 (4)6 (6)10 (10)0.455
Emergency centre4 (4)4 (4)7 (6) 
Required inpatient care0 (0)2 (2)3 (3) 
Reason for re-presentation**   0.961
Endometritis1 (25)2 (33)2 (20) 
Wound infection/dehiscence1 (25)2 (33)3 (30) 
Other***2 (50)2 (33)5 (50) 

There were significant differences between groups in women’s reported pain during insertion of the ripening device or gel (Figure 3A, = 0.002) with double balloon group having higher pain scores than the single balloon and PGE2 group. Further, there were significant differences between groups in women’s reported pain during the cervical ripening phase (Figure 3B, < 0.001) with the single balloon group reporting the least discomfort with 36% reporting a pain score greater than four compared with 63% in the PGE2 group and 55% in the double balloon group (< 0.001). There were no differences between groups in the overall satisfaction with induction of labour (= 0.179) with the median overall satisfaction score of eight out of ten. Multivariable logistic regression analysis showed that caesarean section (OR, 95% CI 4.66, 2.84–7.65), oxytocin infusion (2.20, 1.08–4.52) and gravidity greater than one (0.44, 0.25–0.75) were associated with low satisfaction with induction of labour (VAS < 8).

Figure 3.

 Patient pain and satisfaction scores with mode of induction. Box and whisker plots for visual analogue scores (0–10 with maximum pain or satisfaction scoring 10) assessed 24–48 hours after delivery for (A) pain with insertion of ripening device, (B) pain during cervical ripening and (C) overall satisfaction with induction of labour.

The only difference in cost between the three groups in this study relate to the cost of the cervical ripening device as there were no differences between groups in: length of time in labour ward, mode of delivery, postnatal complications, duration of hospital admission or re-presentation to hospital after discharge. The cost of ripening devices used in the trial were substantially lower for the Foley catheter (AUS$2.00) compared with the ARD double catheter (AUS$81) and PGE2 gel (AUS$124 for two doses).


This study was undertaken to compare the efficacy, safety and patient satisfaction of three methods of induction in nulliparous women with unfavourable cervix: prostaglandin gel, a single Foley catheter and a double balloon catheter. Mechanical methods were as effective as biochemical methods of cervical ripening in nulliparous women undergoing induction of labour and had fewer adverse effects. Caesarean delivery was required in more than a third of births with no difference between modes of cervical ripening.

Furthermore, one quarter of all neonates were admitted to the nursery (which likely reflects local unit policies as many of these admissions were for maternal reasons). There was no difference in nursery admission rates between groups; however, measures of newborn wellbeing were significantly worse for women receiving prostaglandin gel. While no adverse reactions occurred with the single balloon catheter, PGE2 gel for cervical ripening was associated with increased rates of uterine hyperstimulation, FHR pattern abnormalities and an increased need to perform fetal scalp blood sampling. Further, PGE2 gel was associated with increased rates of fetal acidaemia in cord arterial blood collected after delivery with lower pH and pO2 values and higher pCO2 values compared to the mechanical methods of cervical ripening. These data suggest increased rates of respiratory acidosis after cervical ripening with PGE2 gel, probably secondary to the increased rates of uterine hyperstimulation seen with this cervical ripening technique. Although the shift in blood gas distributions towards acidaemia is concerning, of more concern is the observation that four of the five cases of severe acidemia occurred in the PGE2 arm of the study. To our knowledge, this is the first study comparing methods of induction of labour to report umbilical cord blood gases on all neonates at delivery. This study was not powered to address the issue of fetal acidaemia and these results should be viewed with caution. However, the data presented suggest that this is an important outcome for future studies optimising methods of cervical ripening and induction of labour.

Although patient satisfaction scores were similar in the three groups, women reported significantly lower pain scores with the single balloon catheter than either PGE2 or double balloon catheter during the 12–18 hours of cervical ripening. With no difference in effectiveness between ripening methods, it appears that the single balloon Foley catheter is the most cost-effective method of induction with fewer side-effects and a cost substantially less than either the double balloon catheter or PGE2 gel. Although other prostaglandin preparations such as tablets or pessaries are less expensive than PGE2 gel,25 all have similar efficacy and incidence of adverse reactions.7,26

Comparison with previous studies

This study was the first to compare double balloon catheters with both single balloon catheters and a prostaglandin preparation in nulliparous women. We found the double balloon catheter offered no advantage over the single balloon. In contrast, previous case series indicated good success rates;22 however, the findings of two small randomised controlled trials comparing the double balloon catheter to vaginal prostaglandins were equivocal possibly because of small sample sizes and mixed parities.21,23 The present study also found some women experienced pain and difficulty voiding with the double balloon in situ suggesting that the Foley catheter is likely to be more acceptable to women undergoing cervical ripening.

The finding of no difference in caesarean section rates is consistent with previous randomised controlled trials comparing balloon catheters with vaginal prostaglandins.6,9 Similarly, uterine hyperstimulation with prostaglandin induction has been reported previously but differences in neonatal outcomes identified in this study have not been investigated adequately.6,7 In addition to having a larger sample size, the present study was the first to compare these outcomes in a sample restricted to nulliparous women who are known to have less favourable outcomes.10

The absence of effect of either Bishop Score or FFN (on the success of induction of labour or length of labour) may be explained by the inclusion criteria for the study, namely, the requirement of an unfavourable cervix. This contrasted with previous studies of samples with a range of Bishop Scores prior to induction of labour.13,17 Perhaps the reason for the difference in our study is a lack of sensitivity of the Bishop score to success of induction of labour within a subgroup of women with unfavourable cervices. Furthermore the lack of association between FFN and caesarean section is consistent with a previous study of nulliparous women and reflects the differences in induced labour between nulliparous and multiparous women.18

Study limitations

The sample size of this study is modest compared to other studies of induction of labour; however, the focus on nulliparous women with unfavourable cervices provides detailed data on a relatively homogeneous group of women where induction of labour is most challenging. Further, the authors acknowledge that the power calculation could be considered optimistic with this study having 80% power to detect a 50% reduction in the caesarean section rate from 30% to 15%. The predicted 15% caesarean section rate has previously been reported in observational studies using the double balloon catheter.21,22

The PGE2 protocol used in this study is widely used within Australia; however, the dosage regime can result in women receiving up to 6 mg in 24 hours, an amount larger than recommended by the manufacturer and the British RCOG guidelines.2 Of note, the mean number of doses of 2 mg PGE2 gel was 1.8 with only 20% of women in the PGE2 group requiring 3 doses. Moreover, 75% of cases of uterine hyperstimulation occurred with the first dose, 25% with the second and none with the third dose. Further, none of the cases of severe acidosis in this study occurred in women with three doses of PGE2 gel with the neonatal pH values ranging from 7.09 to 7.33 and base excess values ranging from −8.3 to −0.2 mmol/l in this subset of women. These data suggest that the dosage regime is unlikely to be the sole reason for the differences in outcomes between study groups in this study.

The nursery admission rates in this study are high (25%) with no difference between the groups in rate or reason for nursery admission. The nursery admission rate in this study is similar to the admission rate for all neonates from nulliparous women induced at term in our unit over the 3 years of this study (26%) and may reflect local unit policy. For example, one-third of women in this study were induced for pre-eclampsia, many of whom would have received a magnesium sulphate infusion during and after delivery. Local unit policy is for these women to be managed in the adult special care unit post delivery, often with their babies going to the special care nursery.


Our findings highlight the risks associated with induction of labour in nulliparous women with unfavourable cervices. Women should be advised of the high risk of caesarean section and nursery admission when induction of labour is recommended. Furthermore, women’s views on the acceptability of cervical ripening need to be addressed in future studies.27 While our study included only a simple assessment of patient satisfaction, these findings suggest that women preferred the single Foley catheter to either the double balloon catheter or PGE2 gel.


Induction of labour is associated with high rates of maternal and neonatal complications in the nullipara with unfavourable cervix. Outcomes are likely to be considerably improved if induction can be deferred until after ripening has commenced by natural means. When maternal or fetal condition indicates the need for induction of labour, our data suggest that a single balloon catheter is the safest, least expensive and most acceptable method of cervical ripening in nulliparous women with unfavourable cervices.

Disclosure of interests

The authors are financially independent from the funding bodies and have no potential conflict of interest.

Contribution to authorship

CEP (guarantor) conceived and designed the study, prepared the protocol, implemented the intervention, interpreted the data and revised the article. JJH collaborated with study design, and preparation and revision of the article. MJO collaborated in the preparation of the protocol and implementation of the intervention. SM collaborated with preparation of the protocol, data collection and preparation of the article. DAD collaborated with study design, and analysed and interpreted the data. JED collaborated with study design, preparation of the protocol and revision of the article. All authors approved the final version.

Details of ethics approval

Approved by the Ethics Committee of the Womens’ and Childrens’ Health Service, Perth, WA (Registration Number 620/EW).


Supported by a grant from the Women and Infants Research Foundation, King Edward Memorial Hospital, Perth, Australia. Adeza Biomedical Corporation contributed support for the fetal fibronectin test kits.


Jenny Francis (research midwife) assisted with data collection. The authors thank the women who participated in this study.