Sahel Medical Journal

: 2022  |  Volume : 25  |  Issue : 3  |  Page : 67--73

Comparison of two volumes for extra-amniotic Foley catheter balloon inflation at preinduction of labor cervical ripening in nulliparae

Fidelis Oziengbe Ilevbare1, Ignis Osehie Iribhogbe2, Adedapo Babatunde Anibaba Ande2, Nosakhare Osasere Enaruna2,  
1 Department of Obstetrics and Gynaecology, Chesterfield Royal Hospital, Chesterfield, UK
2 Department of Obstetrics and Gynaecology, University of Benin Teaching Hospital, Benin City, Nigeria

Correspondence Address:
Dr. Fidelis Oziengbe Ilevbare
Department of Obstetrics and Gynaecology, Chesterfield Royal Hospital, Chesterfield


Background: The success of induction of labor is dependent on how favorable the cervix is and the unripe cervix thus remains a well-recognized impediment to the successful induction of labor. Objective: The objective is to compare the efficacy of 50 ml versus 30 ml fluid inflation of Foley catheter balloon for cervical ripening in postdate nulliparous women billed for induction of labor. Materials and Methods: A comparative analytical study with randomization involving 88 nulliparous women with postdated pregnancy requiring cervical ripening prior to induction of labor was carried out from January 1, 2018, to August 31, 2018. They were randomized into Group A consisting of women who had 50 ml (study) and B who received 30 ml (control). Bishop score was assessed 12 h later. Data were entered into a pro forma and analyzed using the IBM Statistical Package 20. Results: A total of 88 patients participated in the study. A statistically significant higher mean change in Bishop score was observed in the study group when compared to the control group (5.6 ± 2.5 vs. 3.1 ± 1.6, P = 0.0001), and the difference was statistically significant. Similarly, 41 (93.2%) patients in the study group had a favorable cervix post-ripening, while in the control group, 30 (68.2%) patients had a favorable cervix (P = 0.003). More of the control group had repeat Foley catheter insertion compared to the study group (31.8% vs. 6.8%, P = 0.008). Conclusion: The use of 50 ml of fluid to inflate Foley catheter balloon for cervical ripening improves Bishop score better than the smaller volume of 30 ml.

How to cite this article:
Ilevbare FO, Iribhogbe IO, Ande AB, Enaruna NO. Comparison of two volumes for extra-amniotic Foley catheter balloon inflation at preinduction of labor cervical ripening in nulliparae.Sahel Med J 2022;25:67-73

How to cite this URL:
Ilevbare FO, Iribhogbe IO, Ande AB, Enaruna NO. Comparison of two volumes for extra-amniotic Foley catheter balloon inflation at preinduction of labor cervical ripening in nulliparae. Sahel Med J [serial online] 2022 [cited 2023 Dec 10 ];25:67-73
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Full Text


In many women, labor starts spontaneously and results in vaginal delivery at or near term. Sometimes, because of medical or obstetrics conditions complicating pregnancy, cervical ripening, and induction of labor is often required.

Induction of labor is the artificial initiation of labor process in a pregnant woman after attaining viability of the pregnancy with the aim of achieving vaginal delivery.[1],[2] Induction of labor is indicated when the benefits of delivery to either the mother and/or fetus outweighs those of continuing the pregnancy.[2]

The success of induction of labor is dependent on how favorable the cervix is.[3] The cervix will need further ripening if the Bishop's score is 5 and below. The unripe cervix thus remains a well-recognized impediment to the successful induction of labor.[4]

Pharmacological and mechanical methods are available for cervical ripening. Prostaglandins are the most common pharmacological agent used, while the Foley or Cook balloon catheter are the commonest mechanical methods.[5]

Prostaglandins use is associated with hyperstimulation in 20% of women.[6] These pharmacological methods for cervical ripening are common in developed countries, probably due to its availability, small dosage formulations and ability to remove drug if hyperstimulation occurs. The situation is not the same in sub-Saharan Africa and Nigeria in particular, where these drugs are not readily available (e.g., dinoprostol), and even where they are available, the attendant complications which may be associated with the use for cervical ripening such as hyperstimulation and uterine rupture (e.g., misoprostol) makes the mechanical method of cervical ripening desirable in our environment.

Foley catheter use is safe, cheap, easily accessible and has less complications compared to the pharmacological methods of cervical ripening.[7] One of the major advantages of the use of Foley catheter for cervical ripening is that it ripens the cervix without effective uterine contraction.[8]

Therefore, the possibility of uterine hyperstimulation and its consequences is very minimal compared to prostaglandin use.[1],[8]

Various researchers have attempted to use different volumes of water to inflate the Foley catheter with the assumption that this might improve the Bishop score and avoid the need for repeated passage of Foley catheter.[9] This study compared the use of two different fluid inflation volumes of balloon Foley catheter, to assess any significant change in Bishop Score with larger filling volumes.

 Materials and Methods

This study was conducted at the Obstetrics and Gynaecology Department of the University of Benin Teaching Hospital, Benin City. The annual birth rate is about 2,700 and an average induction of labor rate of about 20%.

Study design

This was a comparative analytical study with randomization conducted at the department of Obstetrics and Gynaecology, University of Benin Teaching Hospital, Benin City, between January 2018 and August 2018.

Inclusion criteria

All consenting nulliparous women billed for induction for postdated pregnancy, singleton fetus, in longitudinal lie, cephalic presentation, with Bishop score <6. A reactive cardiotocograph was mandatory.

Exclusion criteria

Women, who refuse consent, gestation age ≤40 weeks, abnormal lying fetus, prior uterine surgery, premature rupture of membranes. Women with contraindication to vaginal delivery, cervical dystocia, fibrosis, and incompetence were also excluded from the study.

Methods and randomization

The research team consisted of the principal researcher as the leader and research assistants (Senior Registrars and Registrars) who underwent pre-study period of training on Bishop score assessment and extra-amniotic Foley catheter passage for cervical ripening as practiced in the department. The team was divided into two; Team 1 and Team 2. Team 1 consisted of the principal researcher and two other dedicated members (blinded to the volume of fluid used to inflate the Foley balloon), who performed the precervical ripening Bishop score assessment and the postcervical ripening Bishop Score assessment. The same individual performed both assessment for the same patient to limit bias. Team 2 consisted of the other members of the research team who were responsible for patient selection and passage of the Foley catheter by 6 pm the day preceding the day of induction of labor and the removal by 6 am (after 12 h) the morning of induction of labor.

Patients were counseled on the study during their antenatal clinic period and consenting women who met the inclusion criteria were recruited for the study. At presentation in the labor ward a day prior to induction of labor, who recruited patients had their antenatal records cross checked, gestational age of fetus validated and any contraindication to vaginal delivery excluded. A cardiotocograph was done – which has to be reactive for continuity in the study. Initial assessment of subjects included general and obstetric examinations before a sterile vaginal examination to identify those with Bishop Score of <6, who were then selected for the study. Selected patients were divided into two groups; A and B. Group A (study) were patients whose Foley catheter balloon was inflated with 50 ml of sterile water, while group B (control) were patients whose Foley catheter balloon was inflated with 30 ml of sterile water.

An independent research assistant not involved in data collection or analysis must have done prior randomization of patients into two groups using a computer-generated random number table permuted in blocks of 10 with a 1:1 ratio of study subjects to control. Group assignments were kept in the labor ward in sequentially numbered sealed opaque envelops. Consenting eligible patients each picked an envelope that was opened by Research members in team 2 to determine if she would be in the study or control group. Cervical ripening with Foley catheter balloon inflated to the appropriate volume depending on the group-were done at admission into the labor ward by 6 pm on the day of cervical ripening. Both groups of patients were reassessed by vaginal examination (which was done by Researchers in Team 1) to assess the Bishop score of the patients 12 h after Foley catheter insertion (by 6am the morning of Induction of labor). A Bishop score of 6 and above was taken as being favorable.

Study instruments

A designed pro forma/data extraction form, was used to record important demographic information and data collected for each patient. These included age, Bishop score prior to ripening and after ripening, cervical dilatation before and after cervical ripening, and repeated passage of Foley catheter.

Outcome measures

The primary outcome measure was the mean change in the Bishop score, and proportion of women with a favorable Bishop score (after 12 h of cervical ripening) in both the groups. The secondary outcome measures were the proportion of women requiring repeat Foley insertion for cervical ripening, the proportion of women who achieved active phase parameters following cervical ripening in both groups.

Sample size determination

In evaluating effectiveness of cervical ripening with Foley catheter, a previous study (1) showed the effectiveness of a 30 ml inflated Foley catheter used for cervical ripening to be 56.8%. Assuming a 50% increase in effective cervical ripening with use of Foley catheter with balloon inflated to 50 ml, accepting a statistical power of 80%, confidence interval of 90%, with the level of significance set at 0.05 the required sample size was 45 using appropriate formula and attrition rate of 10%:[10]

Data management

Statistical analysis

Data entered were analyzed using [statistical Package for Social Sciences (SPSS)] computer program version 20 (SPSS IBM Corp, Armonk, NY). Means, frequencies, and standard deviation were used to calculate descriptive statistics. Continuous data were expressed as average with standard deviation, and qualitative data as absolute and relative frequency were presented as relative risks with a 95% confident interval. Standard error difference between percentages for two proportions (Z-test) was applied when appropriate. Test of association between continuous variables was done using the Student's t-test while the Chi-square test was used for categorical variables.

Ethical approval

Approval for this study was obtained from the Ethical and Research Committee of the University of Benin Teaching Hospital (ADM/E 22/A/VOL. V11/14521) on August 23, 2017. Also, the study was carefully explained to the patients and written informed consent to participate in the study and for data to be shared for research and publication purposes, obtained from all participants in accordance with Helsinki 2013 declarations.


A total of 88 postdate nulliparous women billed for cervical ripening were recruited for this study; 44 each for the 50 ml and 30 ml Foley catheter balloon inflation volume, respectively.

Ages of participants recruited for the study ranged from 18 to 41 years. Most of the women in both groups were between 20 and 29 years. In that age range, the Group A had 30 (68.2%), while Group B had 25 (56.8%). The mean age was 27.9 + 5.0 years for the Group A (study), while those in Group B (control) had a mean age of 29.5 ± 6.0 [Table 1]. This was not statistically significant (P = 0.187).{Table 1}

Spontaneous expulsion of catheter was seen more in those who had cervical ripening in Group A (study), compared to Group B (control) (40.9% vs. 11.4%, P = 0.002), and this was statistically significant, as shown in [Table 2] below. The median Bishop score after expulsion or removal of catheter was 8.5 and 6 for Group A and Group B, respectively. Similarly, the mean Bishop score after balloon expulsion or removal of catheter for Group A was 9.0 + 2.6 against 6 + 1.6 for Group B which was statistically significant [Table 1] and [Figure 1] and [Figure 2].{Table 2}{Figure 1}{Figure 2}

Forty-one (93.2%) women in the 50 ml group had a favorable cervix post-ripening, against 30 (68.2%) of women in the 30 ml group. This was statistically significant, P = 0.003 [Table 3]. Only 3 (6.8%) of the women in Group A did not have a favorable cervix after ripening, against 14 (31.8%) of women in Group B.{Table 3}

Score ≥6 - FavorableScore <6 - Not favorable.

The mean change in Bishop score after cervical ripening between Group A and Group B (5.6 ± 2.5 vs. 3.1 ± 1.6, P = 0.0001) was statistically significant as shown in [Table 4]. Fewer women in Group A required repeated passage of Foley catheter when compared to those in group B (9.1 vs. 31.8%), this was statistically significant. More of the women in Group A achieved active phase parameter after cervical ripening, when compared to the Group B (31.8 vs. 5.0%). This was statistically significant [Table 4].{Table 4}

Spontaneous vaginal delivery was achieved more in the Group A than Group B (87.8% vs. 57.6%). More emergency cesarean sections were recorded in Group B than those in Group A (33.3% vs. 9.8%). Less instrumental deliveries were recorded in Group A (2.4% vs. 9.1%) compared to Group B [Figure 3].{Figure 3}


The primary aim of induction of labor is to achieve safe vaginal delivery.[2] Cervical favorability is a major determinant of successful vaginal delivery following induction of labor. The induction rate is around 10%–20% in many centers and 10% of the inductions are for pregnancies beyond 41 weeks of gestation,[1] The success of induction of labor depends mainly on parity and cervical favorability.[11] Failed induction of labor thus means an increased cesarean section rate.

The rate of cesarean section has been on the increase over the past few years. Cesarean section is associated with increased days of hospital stay, scar in the uterus, increase in blood loss, need for further surgeries in future pregnancies and many other possible complications. The cesarean section rate for induction of labor tends to be higher than that for spontaneous active phase labor.[12] Thus having a very favorable cervix prior to induction of labor will improve vaginal delivery rate thus reducing the cesarean section rate significantly. This study enlisted only nulliparous women to reduce confounding factors to improve reliability of the study results. Among those recruited for the study, there was no significant difference in the proportion of women as regard age and gestational age.

This study showed that 50 ml is superior to 30 ml for balloon inflation for cervical ripening with Foley catheter. It is associated with better change in Bishop score, less need for reinsertion, higher chance of achieving active phase parameters compared to 30 ml. This implies that a higher inflation volume is more proficient in increasing the Bishop score before induction of labor. This may not be unconnected to the released prostaglandins which are locally produced when the cervix is mechanically stretched, with some inflammatory changes. It may be extrapolated that a higher inflation volume of balloon resulted in more local release of prostaglandins and inflammatory changes, with resultant cervical changes. This may explain the greater mean change in Bishop score seen in the 50 ml group in this study. Similar findings were seen in a study done in Sri Lanka,[1] where a higher inflation volume resulted in a higher mean change in Bishop score among multiparous women (P < 0.01). It may imply that this mean change in Bishop score following inflation with higher filling volumes may be unrelated to parity but rather to the increased stretch force brought about by the 50 ml inflation volume, resulting in more prostaglandin release with resultant cervical pliability.

Also, more of the women in Group A compared to Group B had favorable Bishop scores postcervical ripening (93.2% vs. 68.2%; P = 0.003), which was statistically significant. It may be inferred that the use of a higher balloon inflation volume for cervical ripening confers a significant improvement to the cervical ripening ability of the Foleys catheter. This high cervical favorability finding post ripening with 50 ml is comparable to ripening with 80 ml in Washington,[13] (P = 0.0001) and Egypt[14] (P = 0.03). It may be inferred from this study that similar cervical favorability can be achieved with use of 50 ml rather than 60 ml or 80 ml inflation volumes used in some other studies.[15],[16] This will enhance reduced cost (as a single balloon Foley catheter is used) compared to the very expensive (35 times more expensive) double balloon catheters used in some other studies where higher volumes were used. This may encourage wide spread use due to accessibility and affordability, other than the double balloon catheters that are often used for research purposes due to the cost. This high cervical favorability with 50 ml inflation volume is also comparable to cervical favorability reported in a study where misoprostol was used to ripen the cervix,[17] The advantage of Foley catheter use over misoprostol however, lies in the fact that it is devoid of some of the erratic complications which may be associated with use of misoprostol for cervical ripening. Foley catheter is cheap, easily accessible and associated with fewer rates of hyperstimulation and tachysystole.[15]

The success of induction depends to a large extent depends on the consistency, compliance and configuration of the cervix.[15] The unripe cervix thus remains a well-recognized impediment to the successful induction of labor.[2] If the Bishop score is <6, the cervix thus needs further ripening prior to induction to improve the vaginal delivery rate. Women in Group B compared to Group A, had more need for repeated passage of Foley catheter due to unfavorable Bishop score after first passage (31.8% vs. 6.8%; P = 0.008). This situation of prolonged cervical preparation can occasionally lead to patient anxiety, increased discomfort, more procedural related pain, and occasional iatrogenic rupture of membranes and infection.[18]

The proportion of mothers who transformed to active phase labor after cervical ripening was higher in Group A compared to Group B (31.8% vs. 5.0%; P < 0.05), the difference was statistically significant and similar to findings from a previous study.[19] A characteristic of the use of Foley catheter for cervical ripening is that it mostly ripens the cervix without necessarily causing uterine contractions that can lead to active phase labor,[8] This allows overnight ripening of the cervix, thus avoiding “night obstetrics.” Using a higher inflation volume means that more women will achieve spontaneous active phase labor after cervical ripening compared to 30 ml inflation volume.

Similarly, women who had cervical ripening with Foley catheter balloon inflated to 50 ml had more spontaneous vertex deliveries compared to the 30 ml group (87.8% vs. 57.6%), lesser percentage of emergency cesarean sections (9.8% vs. 33.3%) and instrumental deliveries (2.4% vs. 9.1%). No change in vagina delivery was observed in a similar study,[13] in Washington where multiparas were used. It can be inferred from these findings that when a higher volume of fluid is used for cervical ripening in nulliparous women, majority of them will not require cesarean section, with its associated complications and future obstetric implications.

This study showed that inflating the Foley catheter with 50 ml is associated with more catheter expulsion rates than with 30 ml (40.9% vs. 11.4%; P = 0.002). Spontaneous catheter expulsion is strong evidence that the cervix have been ripened. This finding was similar to finding from a previous study done in Sri Lanka[1] where 45.5% of the 60 ml group had spontaneous catheter expulsion. Howbeit, multiparas were used and the catheter was left for 24 h. It may be inferred that this change is unrelated to parity and duration of catheter stay, but rather more on cervical pliability and dilation produced by the higher inflation volume.

The aim of induction of labor is to achieve a vaginal delivery. It therefore implies that the higher the cervical favorability, the less likelihood that the woman was going to end up with a cesarean section. In this study, most of the women in Group A had a vaginal delivery (87.8%) compared to the 57.6% vaginal delivery rate observed in Group B. This meant a lower cesarean section rate with the higher filling volume (9.8% vs. 33.3%). This was similar to findings from previous studies.[1],[13]. Since most of our postdate women requiring induction of labor are nulliparous women, who form a large proportion of parturients targeted for advancing a policy of reduced cesarean section rate, achieving a better level of cervical favorability with use of 50 ml inflation volume for Foley catheter balloon will be desirable.

Although dedicated individuals were trained to do the cervical assessment before and after ripening, the limitation of this study is Bishop score being a semi-quantitative measurement may be affected by inter observer error. Other studies in similar population would be needed to validate the superiority of 50 ml over 30 ml for inflation of Foley catheter for cervical ripening.


This study showed that the use of 50 ml inflation volume for Foley catheter balloon is more effective in improving cervical favorability when compared to the use of 30 ml inflation volume for cervical ripening. These noticeable effects were observed with a statistically significant higher mean change in Bishop score, cervical favorability post ripening and reduced need for repeat passage of Foley catheter. Inflating the extra-amniotic Foley catheter balloon with 50 ml fluid confers a better preinduction of labor cervical ripening and outcome than 30 ml.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Jegath W, Najimudeen M. Comparison of 30ml and 60ml Foley catheter for cervical ripening. Eur Sci J 2013;9.
2Ande AB, Ezeanochie CM, Olagbuji NB. Induction of labor in prolonged pregnancy with unfavorable cervix: Comparison of sequential intracervical Foley catheter-intravaginal misoprostol and intravaginal misoprostol alone. Arch Gynecol Obstet 2012;285:967-71.
3Bishop EH. Pelvic scoring for elective induction. Obstet Gynecol 1964;24:266-8.
4Rouse DJ, Owen J, Hauth JC. Criteria for failed labour induction: Prospective evaluation of a standardized protocol. Obstet Gynaecol 2000;96:671-7.
5Tenore JL. Methods for cervical ripening and induction of labour. Am Fam Physicians 2003;67:2123-8.
6Sanchez-Ramos L, Kaunitz AM, Wears RL, Delke I, Gaudier FL. Misoprostol for cervical ripening and labor induction: A meta-analysis. Obstet Gynecol 1997;89:633-42.
7Norman JE. Induction and augmentation of labour. In: Dewhurst Textbook of Obstetrics and Gynaecology. 8th ed. Malden, Mass: Blackwell science; 2012. p.287-95.5.
8Trofatter KF, Bowers D, Standby RN, Gal AL, Killam AP. Preinduction cervical ripening with prostaglandin E2 Gel. Am J Obstet Gynecol 1985;153:268-71.
9Berndl A, El-Chaar D, Murphy K, McDonald S. 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. J Obstet Gynaecol Can 2014;36:678-87.
10Altman DG. Practical Statistics for Medical Research. London, UK: Chapman & Hall; 2001.
11Calder AA, Loughney AD, Weir CJ, Barber JW. Induction of labour in nulliparous and multiparous women: A UK, multicentre, open-label study of intravaginal misoprostol in comparison with dinoprostone. BJOG 2008;115:1279-88.
12Ezimokhai M, Nwabineli JN. The use of Foley's catheter in ripening the unfavourable cervix prior to induction of labour. Br J Obstet Gynaecol 1980;87:281-6.
13Hoppe K, Schiff M, Peterson S, Gravett M. Randomized controlled trial: Comparing 80mL double versus 30mL single balloon catheters for pre-induction cervical ripening. Am J Obstet Gynaecol 2014;210:S326.
14Sayed Ahmed WA, Ibrahim ZM, Ashor OE, Mohamed ML, Ahmed MR, Elshahat AM. Use of the Foley catheter versus a double balloon cervical ripening catheter in pre-induction cervical ripening in postdate primigravidae. J Obstet Gynaecol Res 2016;42:1489-94.
15Boulvain M, Kelly AJ, Lohse C, Stan CM, Irion O. Mechanical methods for induction of labour. Cochrane Database Systemic Rev 2001:CD001233.
16Levy R, Kanengiser B, Furman B, Furman B, Arie AB, Brown D, et al. A randomized trial comparing a 30mL and an 80mL Foley balloon for pre-induction cervical ripening. Am J Obstet Gynaecol 2004;191:1632-6.
17Dede FS, Heberal AS, Dede H, Sivaslioglu A, Arslanpence I. Misoprostol for cervical ripening and induction in patients with oligohydramnios. Gynecol Obstet Investig 2004;57:139-43.
18MetroHealth Medical Center. Foley Bulb Traction for Cervical Ripening Available from: [Last accessed on 2013 Jun 07].
19Manish P, Rathore S, Benjamin SJ, Abraham A, Jeyaseenlan V, Mathews JE. A randomized controlled trial comparing 30mL and 80mL in Foley catheter for induction of Labour after previous Caesarean section. Trop Doct 2016;46:205-11.