Research title: Transvaginal
ultrasound measurement of cervical volume prior to induction of labour and its
relationship with outcome of induction of labour
Background and justification
Induction of labour (IOL) is defined as planned
initiation of labour prior to spontaneous onset.1When compared to expectant
management it has shown to reduce peri-natal mortality and morbidity in potentially
compromised foetuses and in certain maternal diseases. In current obstetric
practice approximately 15-20% of women undergo induction of labour due to
various indications.2 Approximately 70% of induced labours
deliver by vaginal delivery without further intervention,
while about 15% need assisted vaginal delivery and 22% need emergency caesarean
Sri Lanka has the highest prevalence of IOL in the region (35%) according to
In addition to failed induction, IOL may also be
associated with adverse outcomes such as uterine hypertonus, uterine rupture,
cord prolapse and fetal distress. Inappropriate patient selection stands as a
leading cause of adverse outcomes and failed induction. Assessment of suitable
candidates based only on digital cervical assessment is one contributing factor
for this. Though the physiological trigger for labour remains uncertain in
human, cervical changes in association with regular uterine contractions is the
‘sine qua non’ (element factor) of labour.4
Digital cervical assessment remains the best
available method of assessing uterine cervix to date. Bishop et al.5 introduced a pelvic
scoring system for elective induction that can be used as a tool to predict the
outcome. However Bishop introduced this scoring system to predict the post
induction outcome in multigravidae, which was later modified with addition of
cervical length instead of effacement. Digital cervical length assessment is a
subjective assessment, which is observer dependent, and shows wide variations
hence difficult to standardize.6
Several recent studies have proposed that
transvaginal sonographic assessment of cervix uteri is more sensitive in
prediction of obstetric outcome in induction of labour7-9.
Almost all these studies assessed the sonographic cervical length, and none of
them measured the cervical volume. Cervical volume calculation includes both
the length and the diameter of the cervix which covers two aspects of cervical
scoring systems. The objective of this study is to comparatively assess the
predictive value of cervical volume in IOL, and to obtain an index cervical
volume, to predict on induction of labour outcome.
1.2 Literature review
in any obstetric intervention it is the paramount importance to ensure that the
indication for induction of labour still exists. Assessment of the states of
uterine cervix remains the most reliable indicator of success at induction of
labour. There are several previous studies which have shown association between
sonographic cervical length and induction delivery interval. Most of these
studies compared Bishop score system with sonographic assessment and some of
the results are conflicting.
et al.10 examined 86 women
prior to induction and found significant associations between both the Bishop
score and sonographically measured cervical length with successful induction of
labour and the induction to delivery interval.
et al.11 examined 50 study
participants prior to induction and reported that, Bishop score associate
significantly with successful vaginal delivery but the score does not
satisfactorily predict the outcome of induction of labour. In addition they
reported cervical volume measured sonographically, was not significantly associated
with either the Bishop score or induction to delivery interval. However the
sample size of this study was small since it was done as a pilot study.
et al.12 examined 53 women
prior to induction and found that, although sonographically measured cervical
length correlated with the duration of the latent phase of labour , there was
no significant association with the induction to delivery interval. Since the
study sample was small the predictive value of the cervical length measurement
in success of IOL could not be elicited in this study.
et al.8 carried out
pre-induction sonographic measurement of cervical length in the prediction of
successful induction of labour, in a relatively larger sample (n=240) and
concluded that both sonographic cervical length assessment and the Bishop score
successfully predicted vaginal delivery within 24h from start of induction.
They reported that the cervical length appears to be a better predictor than
the Bishop score, with a sensitivity of 0.87 and a specificity of 0.71 compared
to 0.58 and 0.77 for digital assessment. Although the study compared the
score with ultrasonic cervical length assessment, the dilatation of the
endocervical canal and the width of the cervix were not measured. Since Bishop
score incorporates the degree of effacement of the cervix, above two parameters
remain important to compare the two systems.
is hypothesized that these shortcomings can be prevented by the assessment of
cervical volume, instead of cervical length alone, since the former measures
both the cervical dilatation and the width.
02. Objectives of the study
2.1 General Objective:
a cutoff for a favorable cervical volume for induction of labour and to assess
the predictive value of cervical volume measurement in successful induction of
2.2 Specific Objectives:
To describe the mean
volume of cervix at term and its variability with parity
To obtain a cut off
cervical volume as an index to predict success at induction of labour.
To compare cervical
volume with Modified Bishop Score for assessing favorability of cervix in IOL.
To compare the
predictive values of sonographic cervical length and cervical volume for
success at IOL
3.1 Study design
This would be a cross sectional study on a sample of
women undergoing induction of labour after completing 37 weeks of POA.
study will be carried out
Study population would be selected from
women who are admitted for induction of labour to the study unit. Pre induction
cervical assessment will be done by both the modified Bishop score and
transvaginal ultrasound. Suitable women who fulfil following criteria will be
included in the study after informed written consent.
· Singleton pregnancy
· Term pregnancy at 37-42 gestation
· Previous uterine scar
· Pre labour rupture of membranes
· Evidence of fetal distress
· Previous cervical surgeries- LLETZ, cone
biopsy or cervical circlage.
· Any condition that contraindicates the unit
protocol of induction of labour
3.4.1 Ultrasonic cervical assessment
induction ultrasonographic cervical volume assessment will be carried out
within 30 minutes of decision for IOL.
Cervical volume assessment will be done by a single investigator with
expertise and accreditation on ultrasound scanning.
subjects will be made comfortable in dorsal recumbent position. They will be
advised to empty the bladder immediately prior to the assessment and the
transvaginal probe will be placed in the vagina one to two centimetres away
from the cervix with minimal pressure to avoid angulations and distortion of
its cylindrical geometry.
ultrasound will be performed with a sector phased array 7 MHz probe (Sonoscape,China),
offset at 30 degrees to give a field of view of 90 degrees11.
Adequate amount of sterile contact jelly will be applied both inside and
outside of the disposable sterile condom. Sagittal view of the cervix will be
obtained and internal and external os would be identified with the echogenic
endocervical mucosa adjoining them. Cervical length will be measured by
“tracing” the distance between internal and external os, the furthest points at
which cervical walls were juxtaposed.7,13,14.
The ‘trace’ option of the ultrasound machine will be used for this measurement.
Shortest cervical length of three consecutive measurements would be documented
in order to minimize the effect of funnelling13.
Measurement of antero-posterior diameter
of the cervix will be obtained at the midpoint of the cervix, right angled to
the endocervical canal
Cervical volume would be assessed
assuming the cervix is a cylinder in geometric view.
When cervix is dilated, volume will be
calculated by deducting the volume of the dilated tunnel from the total volume.
Digital cervical assessment
Pre induction Modified Bishop Score will
be assessed by an experienced member of the obstetric team who is unaware of
the sonographic findings.
Induction of labour
Induction of labour will be performed
according to the unit policy based on WHO recommendations for IOL issued in
20113. Those with an unfavourable cervix
(Bishop score <3) will be offered induction of labour with Foley catheter insertion, where the catheter will be passed through the cervical canal and the balloon is inflated with 50ml of distilled water. The catheter will be left in place until it drops out or up to 48 hours15. At the end of this time the vaginal examination will be repeated and either Prostaglandin (PGE2) or amniotomy would be offered according to cervical favourability. Those with a more favourable Bishop score (3-7) at the beginning will be offered Dinoprostone 3mg extended release vaginal tablet over 24 hours. If the score is more than 7 artificial rupture of membrane will be performed and oxytocin augmentation is started if the progress of labour is not satisfactory. Failed induction will be diagnosed when labour is not established or when cervix is not suitable for ARM, after one cycle of PGE2 controlled released pessary over 24 hour duration. When amniotomy has been performed, if the cervix fails to dilate beyond 3cm in 6 hours despite stimulation with maximal infusion rate of oxytocin for 6 hours, induction failure will be diagnosed16. 3.4.4 Clinical endpoints of the study The study end points would be the delivery of the baby. All events up to that would be recorded and used as outcome variables, as needed. 3.5 Sample size calculation The sample size calculation was done based on the findings of Park, where the relationship between cervical length measured by ultrasound and failure of labour induction was studied. WinPepi statistical computer software will be used for calculations. Park observed in his study the cervical length to be significantly different between successful and failed inductions with a mean length of 25.5(SD6.4) mm and 30.2(SD7.3) mm, respectively17. In the absence of any studies using cervical volume this data was used since the cervical length closely correlates with the cervical volume. In order to detect a minimum difference of 5mm3 in the cervical volume, with a study power of 80% at a significance level of 5% a minimum of 31 subjects in each group would be required. In their study the failure rate for IOL was 55/161 that is approximately 1:2. Therefore in order include a minimum 31 in the IOL failure group we will need to recruit up to 93 in this cross sectional study design. There are no drop out are anticipated since the analysis would be on an 'intention to treat' basis. However, to compensate for any variations on the assumptions made on the rate of failure, 120 women will be recruited for the study thus 40 women will be in the induction failure group. 3.6 Outcome measures 1. Distribution of cervical volume in term pregnancy. 2. Distribution of Bishop score in term pregnancy. 3. Induction delivery interval. - Time duration from the beginning of any of the above modalities of IOL, to delivery of the baby. 4. Number of failed inductions. – as defined in methodology 5. Number of assisted vaginal deliveries. 6. Number of Caesarean section. 3.7 Data collection Simultaneous data collection will be done in separate, comprehensive data collection sheets for each study participants, during cervical assessment. Induction outcome will be recorded in the same sheet. 3.7 Statistical analysis and plan of presentation of results The data analysis would be at the conclusion of the study. The measurements of pre induction cervical volume will be used for development of reference charts for cervical volume at term between primiparous and multiparous women. The correlation between Bishop score and the cervical volume would be calculated using Spearman correlation coefficient. A cutoff level for cervical length to predict success at induction of labour would be calculated using a ROC curve and the value thus derived would be compared with the bishop score recommendations using positive predictive and negative predictive values by 2x2 tables. A significance level of 5% will be used in all data analysis and 95% confidence interval would be used with mean or median, as appropriate. 04. Ethical considerations As the study does not alter or substitute any standard management protocols it does not affect the routine care of the study subjects. Each study participant would have to undergo an additional transvaginal ultrasound examination that might cause some discomfort in some women. Several previous studies have shown that their study participants have experienced less discomfort during sonographic cervical assessment, compared to digital vaginal examination11. Such ultrasound scanning has not shown to cause any harm to either the baby or the mother and is considered safe during third trimester of pregnancy. Since the PROM is an exclusion criterion for the study, risk of iatrogenic chorioamnionitis presumed to be minimal. As defined in methodology, the probe is kept 1-2cm away from the external os and therefore the risk of rupturing of membranes during procedure is minimized. However a prime attention will be given during probe insertion to avoid such hazards. All study participants will have to undergo a brief clinical interview and no other interventions planned. There will be no additional cost to the patients in view of study participation and there will be no payment of incentives. Ethical approval for the study will be obtained and subsequent permission will be taken from the Medical Director of the hospital. High confidentiality of the patient data is maintained throughout the study period and thereafter, and the data will be used for the purpose of this study only. 05. References 1. Philip N. Baker ed. Obstetrics by Ten Teachers, eighteenth edition: London; Hodder Arnold publications,2006 2. NICE. Induction of labour. Clinical Guideline 70.London: National Institute for health and Clinical Excellence,2008 3. WHO. Recommendations for induction of labour.Guidelines.World Health Organization,2011 4. Gonik B, Creasy RK. Preterm labour,its diagnosis & management. Am J Obstet Gynaecol 1986;154:3-8 5. Bishop EH, Pelvic scoring for elective induction. Obstet Gynaecol 1964;24:266 6. RCOG. Induction of labour. In Evidence-based Clinical Guideline Number 9. London: RCOG Clinical Support Unit, 2001 7. Sonek J, Shellhaas C. Cervical sonography: a review. Ultrasound Obstet Gynecol 1998; 11: 71–8 8. G.K Pandis, A.T Papageorghiou, V.G Ramanathan et al. Preinduction sonographic measurement of cervical length in the prediction of successful induction of labour.Ultrasound Obstet Gyncol 2001;18:623-628 9. Watson WJ, Stevens D, Welter S, Day D. Factors predicting successful labour induction. Obstet Gynecol 1996; 88: 990–2 10. Gonen R, Degani S, Ron A. Prediction of successful induction of labor: comparison of transvaginal ultrasonography and the Bishop score. Eur J Ultrasound 1998; 7: 183– 11. Paterson-Brown S, Fisk NM, Edmonds DK, Rodeck CH.Pre-induction cervical assessment by Bishop score and trans vaginal ultrasound. Eur J Obstet Gynaecol Reprod Biol 1991;40:17-23 12. Boozarjomehri F, Timor-Tritsch I, Chao CR, Fox HE. Transvaginal ultrasonographic evaluation of the cervix before labor: presence of cervical wedging is associated with shorter duration of induced labor. Am J Obstet Gynecol 1994; 171: 1081–7 13. Sonek JD, Iams JD, Blumenfeld M, Johnson F, Landon M, Gabbe S. Measurement of cervical length in pregnancy: comparison between vaginal ultrasonography and digital examination. Obstet Gynecol1990; 76: 172–5 14. Anderson HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol 1990; 163: 859–67 15. Boulvain M et al. Mechanical methods for induction of labour. Cochrane Database of Systematic Reviews, 2001, Issue 4. Art. No.: CD001233; DOI: 10.1002/14651858.CD001233Friedman EA, Niswander KR, Bayonet-Rivera NP et al. Relation of prelabour evaluation to inducibility and the course of labour. Obstet Gynecol 1966;28:495-501 16. David M Luesly and Philip N Baker ed. An evidence-based text for MRCOG, second edition, London: Edward Arnold publications; 2010 17. G. Ranmanathan, C. YU, E. Osei and K. H. Nicolaides. Ultrasound examination at 37 weeks' gestation in the prediction of pregnancy outcome: the value of cervical assessment Ultrasound Obstet Gynecol 2003; 22: 598–603 18. Mozurkewich E ,Chilimigras J, Koepke E et al. Indic ations for induction of labour: a best-evidence review.BJOG, An International Journal of Obstetrics & Gynaecology, 2009, 116:626–636 19. Ulmsten U. Some physical and pharmacological aspects of cervical ripening in term pregnancy. Eur J Obstet Gynecol Reprod Biol 1988; 28:90-94 20. Dhall K, Mittal SC, Kumar A. Evaluation of pre-induction scoring systems. Aust NZ J Obstet - Gynaecol1987; 27; 309-311. 21. Lange AP, Secher NJ, Westergaard JG et al. Prelabour evaluation of inducibihty. Obstet Gynecol 1982; 60:137-147 Calder AA. Prerequisites of preincubation and induction of labour. Eur J Obstet Gynecol Reprod Biol 1983;15;322-324. 22. Ware V, Raynor D. Transvaginal ultrasonographic cervical measurement as a predictor of successful labor induction. Am J Obstet Gynecol2000; 182: 1030–2 23. Cole RA, Howie PW, Magnaughton MC. Elective induction of labour. A randomised prospective trial. Lancet 1975; 1: 767–70 24. Sandek HA, Tuveng J, Fonstelien T. A prospective randomised study of induction of labor. Int J Gynaecol Obstet 1983; 21: 333–6 06. Work Plan 6.1 Work Schedule Task to be performed Dates Persons assigned to task Finalize the research proposal and literature review Week 1-4 Research team 1. Clearance from authorities Week 4-5 2. Ethical Clearance Week 4-7 Research team & ethical committee Training of data collectors/ group members Week 4-5 Supervisor & Fetal medicine specialist 3. Data collection Weeks 7-25 Research team 4. Data Entry Weeks 7-25 Research team 5. Data Analysis Weeks 25-30 Statistician & Research team 6. Report finalization Weeks 30-32 Research team Table 6.1: Work Schedule 6.2 The Gantt chart Task to be performed Responsible person May June July August September Finalize the research proposal and literature review Research team Clearance from authorities Research team Ethical Clearance Research team & ethical committee Training of data collectors/ group members Supervisor Data collection Research team Data Entry Research team Data Analysis Statistician & Research team Report finalization Research team Table 6.2: The GANTT chart