Bishop score: a poor diagnostic test to predict failed induction versus vaginal delivery

Digital Examination vs. 4D Transperineal Ultrasound-Do They Compare in Labour Management? A Pilot Study

The aim was to compare transperineal ultrasound (TPU) with parameters of the Bishop Score during the first stage of labour and evaluate how TPU can contribute towards improving labour management. Digital examination (DE) and TPU were performed on 42 women presenting at the labour ward with regular contractions. TPU measurements included the head-symphysis distance, angle of progression, diameter of the cervical wall, cervical dilation (CD) and cervical length (CL). To examine if TPU can monitor labour progress, correlations of TPU parameters were calculated. Agreement of DE and TPU was examined for CL and CD measurements and for two groups divided into latent (CD < 5 cm) and active stages of labour (CD ≥ 5 cm). TPU parameters indicated a moderate negative correlation of CD and CL (Pearson: r = -0.667; Spearman = -0.611). The other parameters showed a weak to moderate correlation. DE and TPU measurements for CD showed better agreement during the latent stage than during the active stage. The results of the present study add to the growing evidence that TPU may contribute towards an improved labour management, suggesting a combined approach of TPU and DE to monitor the latent first stage of labour and using only DE during the active stage of labour.

Term induction of labour in nulliparous women: When to draw the line?

Objective

Study design

Results

Conclusion

Contribution of ultrasonography to the prediction of the induction-delivery interval: The ECOLDIA prospective multicenter cohort study

INTRODUCTION

To evaluate the ability of preinduction ultrasonographic cervical length to predict the interval between induction and delivery in women at term with a Bishop score of 4 to 6 at induction.

STUDY DESIGN

This multicenter prospective observational cohort recruited 334 women from April 2010 to March 2014. Inclusion criteria were women with singleton pregnancies at a gestational age ≥37 weeks, with no previous caesarean, a medical indication for induction of labor, and a Bishop score of 4, 5, or 6. All women underwent cervical assessment by both transvaginal ultrasound and digital examination (Bishop score). The induction protocol was standardized. The primary outcome measure was the induction-delivery interval. Hazard ratios (HR) and their 95% confidence intervals (95% CI) were used to assess potential predictors.

RESULTS

Mean gestational age at induction was 40.1 weeks, 60.8% of the women were nulliparous, and the cesarean rate was 13.4%. The mean induction-delivery interval was 20.8 h (± 10.6). Delivery occurred within 24 h for 56.9% (n=190) of the women. An ultrasonographic cervical length measurement less than 25 mm (HR=1.50, 95% CI 1.18-1.91, P<0.01) and parity (HR=1.41, 95% CI 1.21-1.65, P<0.01) appeared to predict induction-delivery interval. The cervical length cutoff to reduce the induction-delivery interval was 25 mm.

CONCLUSION

A cervical length cutoff of 25 mm was associated with shorter induction-delivery interval in women at term with a Bishop score of 4 to 6.

The usefulness of ultrasound before induction of labor

The indications for induction of labor have been consistently on the rise. These indications are mainly medical (maternal or fetal) or social or related to convenience or maternal preferences. With the increase in the prevalence of these indications, the incidence rates of induction of labor are expected to rise continuously. This poses a substantial workload and financial burden on maternity healthcare systems. Failure rates of induction of labor are relatively high, especially when considering the maternal, fetal, and neonatal risks associated with emergency cesarean deliveries in cases of failure. Therefore, it is essential for obstetricians to carefully select women who are eligible for induction of labor, particularly those with no clinical contraindication and who have a reasonable chance of ending up with a successful noncomplicated vaginal delivery. Ultrasound has an established role in the various areas of obstetrical care. It is available, accessible, easy to perform, and acceptable to the patient. In addition, the learning curve for skillful obstetrical ultrasound scanning is rather easy to fulfill. Ultrasound has always had an important role in the assessment of maternal and fetal well-being. Indeed, it has been extensively explored as a reliable, reproducible, and objective tool in the management of labor. In this review, we aimed to provide a comprehensive update on the different applications and uses of ultrasound before induction of labor for the prediction of its success and the potential improvement of its health-related maternal and fetal outcomes.

Can We Use the Bishop Score as a Prediction Tool for the Mode of Delivery in Primiparous Women at Term Before the Onset of Labor?

The Bishop score serves as an evaluation system performed by digital vaginal examination (DVE) to determine cervical ripening. The scoring system includes cervical dilatation, position, effacement and consistency of the cervix and fetal head station1. Nowadays, the Bishop score is frequently used as an important parameter for the prediction of successful induction of labor.

OBJECTIVE

Our objective was to demonstrate the role of the Bishop scoring system in prediction of the mode of delivery in primiparous women at term before the onset of labor.

METHOD

We included in this study unselected primiparous women at term, after 37 weeks of gestation, who presented to the Prenatal Diagnostic Unit (PDU) of the University Emergency County Hospital of Craiova. We excluded from the study multiparous patients, pregnancies with a planned Caesarean section delivery (CD), non-cephalic presentations and multiple pregnancies, twin pregnancies and those with detected fetal anomalies. The protocol included weekly DVEs until delivery for all patients, to determine the evolution of the Bishop score at term and in the week before delivery, and potential correlations with delivery outcome. To reduce clinical bias, the DVEs were performed by three experienced obstetricians involved in the research.

RESULTS

Statistical analysis yielded a 4 to 6 Bishop score in all weekly examinations. At 37 weeks of gestation, the majority of primiparous women had a Bishop score of 4, with no significant differences between the primiparous who delivered vaginally and the ones where Caesarean section was necessary. During the following weekly evaluations, we noted a slight turn to a Bishop score of 6 for most of them, without any significant differences between the two groups. However, at 41 weeks of gestation, there was a significant higher Bishop score in the group of primiparous women who delivered vaginally.

CONCLUSION

In our study, the use of the Bishop score failed as a prediction tool for the mode of delivery in primiparous women at term before the onset of labor, at a gestational age less than 40 weeks. Therefore, Bishop score should not be used to counsel regarding the probability of an uncomplicated vaginal delivery (VD) before the onset of labor.

Predicting labor induction success by cervical funneling in uncomplicated pregnancies

Aim

Predictive accuracy of cervical funneling for successful vaginal delivery prior to labor induction was compared to that of conventional methods such as Bishop score and cervical length.

Methods

Prospective observational study was conducted on nulliparous women at 38 gestational weeks or more with intact membranes who delivered vaginally following labor induction. Transvaginal ultrasound was performed prior to labor induction to evaluate the cervix, to determine the cervical length and to check for the presence of funneling. Following pelvic examinations, the Bishop score was calculated. Predictive accuracy of the three different methods, namely cervical funneling, cervical length and Bishop, were compared.

Results

A total of 235 nulliparous women with intact membranes were recruited. Of these, 194 women (82.6%) had successful vaginal deliveries following induction. Cervical funneling was observed in 105 women (44.7%). The rate of successful vaginal delivery was significantly higher in women with cervical funneling than in those without funneling (90.5% vs 76.2%, P < 0.004). Multivariable analysis showed that cervical funneling, similar to traditional measures such as the Bishop score and cervical length, was an independent predictor of successful vaginal delivery following labor induction (odds ratio = 2.95; 95% confidence interval: 1.38–6.47; P = 0.007).

Conclusions

Similar to the conventional methods of cervical evaluation, such as the Bishop score and cervical length, cervical funneling may serve as a useful and valid predictor of successful vaginal deliveries prior to labor induction.

Externally Validated Score to Predict Cesarean Delivery After Labor Induction With Cervi Ripening

OBJECTIVE

To build a score to predict the risk of cesarean delivery after labor induction with cervical ripening, and to compare its predictive capacities with other already existing scores.

METHODS

This study is a secondary analysis of data collected in the prospective multicenter observational French population-based cohort study Methods of Induction of Labor and Perinatal Outcomes, the primary objective of which was to obtain national data regarding labor induction practices in 94 maternity units. A total of 1,692 patients were randomly split into a derivation data set of 1,024 patients (60%) and an internal validation set of 668 patients (40%). Statistical analyses were performed using a Bayesian approach, allowing the use of priors (ie, previous results published in the literature). The final score is a simplified 50-point score. The score was validated using the internal validation set and an external data set of 4,242 patients from the National Institutes of Health's Consortium for Safe Labor database. We compared the area under the curve (AUC) of our score with two other scores: the modified Bishop score and the Levine score, which is a recently published risk calculator for cesarean delivery after labor induction with unfavorable cervix.

RESULTS

In the multivariate analysis, height, body mass index, gestational age, parity, dilation, effacement, fetal head station, medical indication, suspicion of macrosomia, premature rupture of membranes and concerning fetal status were found to be strongly associated with cesarean delivery. The AUC in the derivation set and internal validation set were 0.76 (0.73-0.79) and 0.74 (0.70-0.78), respectively. On the external validation set, the AUC for the present score, the Levine score, and the modified Bishop score were 0.81 (0.79-0.82), 0.76 (0.75-0.78), and 0.74 (0.73-0.76), respectively.

CONCLUSION

Our easy-to-use, externally validated score is efficient in predicting cesarean delivery after labor induction with cervical ripening.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT02477085.

Prediction models for determining the success of labor induction: A systematic review

INTRODUCTION

The purpose of this study was to systematically identify and compare clinical models using universally accessible clinical and demographic factors that were derived and/or validated to predict the success of labor induction with a view to making recommendations for practice.

MATERIAL AND METHODS

MEDLINE, Embase, www.clinicaltrials.gov, and PubMed (for non-MEDLINE and studies in-progress) were searched from inception to November 2017. Only studies that derived and/or validated clinical prediction models using variables obtained through antenatal history and digital cervical examination were included. Two reviewers independently screened titles and abstracts and extracted data from eligible studies into a standardized form. Extracted data included: participant characteristics, sample size, variables considered and included, endpoint definitions, study design and model performance. The Prediction Study Risk of Bias Assessment Tool (PROBAST) was used to appraise included studies. In view of clinical and methodologic heterogeneity between studies, only descriptive analysis was possible. The protocol was registered with the PROSPERO International prospective register of systematic reviews [CRD42017081548].

RESULTS

The search identified 16 studies describing 14 prediction models derived between 1966 and 2018. Models varied and demonstrated major limitations with regard to methodology, scope and performance. Of the derived models, six were internally validated and three were externally validated. Performance was most commonly measured using the area under the receiver operator characteristic curve, which ranged from 0.68 to 0.79, 0.67 to 0.77 and 0.61 to 0.73 for derived, internally validated and externally validated models, respectively. The risk-of-bias of included studies ranged from some studies fulfilling only 36% and some others fulfilling 86% of eligible PROBAST items.

CONCLUSIONS

No published model can be recommended for use at the bedside to determine the success of vaginal birth after labor induction. Based on the limitations of included models, a list of recommendations for improving model performance and utilization is provided, as well as measures for encouraging appropriate use of prediction models. The attitudes of women and care providers, and the clinical and resource implications must be explored prior to recommending the use of prediction models for determining the success of labor induction.

Ultrasound cervical length measurement in prediction of labor induction outcome

Induction of labor is one of the most common procedures in modern obstetrics, with an incidence of approximately 20% of all deliveries. Not all of these inductions result in vaginal delivery; some lead to cesarean sections, either for emergency reasons or for failed induction. That's why, It seems necessary to outline strategies for the improvement of the success rate of induced deliveries. Traditionally, the identification of women in whom labor induction is more likely to be successful is based on the Bishop score. However, several studies have shown it to be subjective, with high variation and a poor predictor of the outcome of labor induction. Transvaginal sonography for cervical measurement can be a more objective criterion in assessing the success of labor induction. Many studies have been done recently to compare cervical measurement and Bishop Score in labor induction.This paper reviewed the literature that evaluated sonographic cervical length measurement to predict induction of labor outcome.

Prediction of labor onset type: Spontaneous vs induced; role of electrohysterography?

BACKGROUND AND OBJECTIVE

Induction of labor (IOL) is a medical procedure used to initiate uterine contractions to achieve delivery. IOL entails medical risks and has a significant impact on both the mother's and newborn's well-being. The assistance provided by an automatic system to help distinguish patients that will achieve labor spontaneously from those that will need late-term IOL would help clinicians and mothers to take an informed decision about prolonging pregnancy. With this aim, we developed and evaluated predictive models using not only traditional obstetrical data but also electrophysiological parameters derived from the electrohysterogram (EHG).

METHODS

EHG recordings were made on singleton term pregnancies. A set of 10 temporal and spectral parameters was calculated to characterize EHG bursts and a further set of 6 common obstetrical parameters was also considered in the predictive models design. Different models were implemented based on single layer Support Vector Machines (SVM) and with aggregation of majority voting of SVM (double layer), to distinguish between the two groups: term spontaneous labor (≤41 weeks of gestation) and IOL late-term labor. The areas under the curve (AUC) of the models were compared.

RESULTS

The obstetrical and EHG parameters of the two groups did not show statistically significant differences. The best results of non-contextualized single input parameter SVM models were achieved by the Bishop Score (AUC= 0.65) and GA at recording time (AUC= 0.68) obstetrical parameters. The EHG parameter median frequency, when contextualized with the two obstetrical parameters improved these results, reaching AUC= 0.76. Multiple input SVM obtained AUC= 0.70 for all EHG parameters. Aggregation of majority voting of SVM models using contextualized EHG parameters achieved the best result AUC= 0.93.

CONCLUSIONS

Measuring the electrophysiological uterine condition by means of electrohysterographic recordings yielded a promising clinical decision support system for distinguishing patients that will spontaneously achieve active labor before the end of full term from those who will require late term IOL. The importance of considering these EHG measurements in the patient's individual context was also shown by combining EHG parameters with obstetrical parameters. Clinicians considering elective labor induction would benefit from this technique.

Simplified Bishop score including parity predicts successful induction of labor

OBJECTIVE

Our objectives were to confirm the predictiveness of parity for successful labor induction and propose an improvement in the Bishop's score to take parity into account and simultaneously simplify the original Bishop score.

STUDY DESIGN

Retrospective study of 326 deliveries induced by oxytocin and amniotomy before prostaglandins between January 1, 1987, and June 30, 1988. We conducted a univariate and then a multivariate analysis of the relation between successful labor induction - defined by vaginal delivery- and the components of Bishop's score and parity.

RESULTS

Nulliparous accounted for 38% of the studied population. The mean Bishop at induction was 5.75±1.4. Fetal station, cervical effacement, and parity were the only factors associated with the success of induction in this study. Removing the cervical position and consistency from the score as well as adding parity significantly improved the prediction of success (ROC curves, AUC 0.88 vs 0.68, p<0.001). By taking 5% as the maximum risk of induction failure, a cutoff point of 4 for the new score makes it possible to induce labor in 90% of the women that were considered in the study (vs 26% or 60%, according to whether the cutoff point of the original Bishop's score is set, respectively, at 7 or 6, p<0.001).

CONCLUSION

Cervical position and consistency are not necessary for predicting successful labor induction by oxytocin and amniotomy. We confirmed the usefulness of a simplified Bishop score that considers parity.

[Are ultrasound measurements of the cervical length and fetal head-perineum distance predictive of delivery outcome in post-term pregnancies?]

OBJECTIVE

Post-term pregnancy is frequently associated with higher fetal and maternal morbidity and mortality. Its management essentially depends on clinical cervical characteristics as evaluated by the Bishop score (BS). However, BS is poorly predictive of the delivery outcome. We sought to demonstrate that ultrasound measurement of cervical length and evaluation of fetal height could predict the outcome in post-term pregnancies.

METHODS

A prospective single center study was undertaken between the 21st of January and the 1st of June 2013. Fetal height was measured using a transperineal technique and cervical length was evaluated by a vaginal ultrasound on patients consulting and their term date. C-section rates were considered to be the primary judgment criteria.

RESULTS

A total of 136 patients were included. C-section rates in this population was 19%. Fetal height and cervical length were not different between the C-section group and the vaginal delivery group.

CONCLUSION

Our study demonstrates that ultrasound measurement of cervical length and fetal height do not show better results than BS in predicting the outcome of post-term pregnancy. Combining these ultrasound measurements has already been suggested in other studies and promising results have been shown. More studies are necessary to further these results.

Methods for assessing pre-induction cervical ripening

BACKGROUND

Induction of labour is the artificial initiation of labour in a pregnant woman after the age of fetal viability but without any objective evidence of active phase labour and with intact fetal membranes. The need for induction of labour may arise due to a problem in the mother, her fetus or both, and the procedure may be carried out at or before term. Obstetricians have long known that for this to be successful, it is important that the uterine cervix (the neck of the womb) has favourable characteristics in terms of readiness to go into the labour state.

OBJECTIVES

To compare Bishop score with any other method for assessing pre-induction cervical ripening in women admitted for induction of labour.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 March 2015) and reference lists of retrieved studies to identify randomised controlled trials (RCTs).

SELECTION CRITERIA

All RCTs comparing Bishop score with any other methods of pre-induction cervical assessment in women admitted for induction of labour. Cluster-RCTs were eligible for inclusion but none were identified. Quasi-RCTs and studies using a cross-over design were not eligible for inclusion. Studies published in abstract form were eligible for inclusion if they provided sufficient information.Comparisons could include the following.1. Bishop score versus transvaginal ultrasound (TVUS).2. Bishop score versus Insulin-like growth factor binding protein-1 (IGFBP-1).3. Bishop score versus vaginal fetal fibronectin (fFN).However, we only identified data for a comparison of Bishop score versus TVUS.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the trials for inclusion, extracted the data and assessed trial quality. Data were checked for accuracy.

MAIN RESULTS

We included two trials that recruited a total of 234 women. The overall risk of bias was low for the two studies. Both studies compared Bishop score withTVUS.The two included studies did not show any clear difference between the Bishop score and TVUS groups for the following main outcomes: vaginal birth (RR 1.07, 95% CI 0.92 to 1.25, moderate quality evidence), caesarean delivery (RR 0.81, 95% CI 0.49 to 1.34, moderate quality evidence), neonatal admission into neonatal intensive care unit (RR 1.67, 95% CI 0.41 to 6.71, moderate quality evidence). Both studies only provided median data in relation to induction-delivery interval and reported no clear difference between the Bishop and TVUS groups. Perinatal mortality was not reported in the included studies.For the review's secondary outcomes, the need for misoprostol for cervical ripening was more frequent in the TVUS group compared to the Bishop score group (RR 0.52, 95% CI 0.41 to 0.66, two studies, 234 women, moderate quality evidence). In contrast, there were no clear differences between the Bishop scope and TVUS groups in terms of meconium staining of the amniotic fluid, fetal heart rate abnormality in labour, and Apgar score less than seven. Only one trial reported median data on the induction-delivery interval and induction to active phase interval, the trialist reported no difference between the Bishop group and the TVUS group for this outcome. Neither of the included studies reported on uterine rupture.

AUTHORS' CONCLUSIONS

Moderate quality evidence from two small RCTs involving 234 women that compared two different methods for assessing pre-induction cervical ripening (Bishop score and TVUS) did not demonstrate superiority of one method over the other in terms of the main outcomes assessed in this review. We did not identify any data relating to perinatal mortality. Whilst use of TVUS was associated with an increased need for misoprostol for cervical ripening, both methods could be complementary.The choice of a particular method of assessing pre-induction cervical ripening may differ depending on the environment and need where one is practicing since some methods (i.e. TVUS) may not be readily available and affordable in resource-poor settings where the sequelae of labour and its management is prevalent.The evidence in this review is based on two studies that enrolled a small number of women and there is insufficient evidence to support the use of TVUS over the standard digital vaginal assessment in pre-induction cervical ripening. Further adequately powered RCTs involving TVUS and the Bishop score and including other methods of pre-induction cervical ripening assessment are warranted. Such studies need to address uterine rupture, perinatal mortality, optimal cut-off value of the cervical length and Bishop score to classify women as having favourable or unfavourable cervices and cost should be included as an outcome.

The role of sonographic cervical length in labor induction at term

The purpose of this study is to review the literature examining the role of ultrasound in the induction of labor. Databases including Ovid, PubMed, Web of Science, Google Scholar, and UpToDate were searched and current guidelines from the SOGC, the ACOG, the RCOG, and the RANZCOG were reviewed. Although studies have not demonstrated the superiority of cervical sonography to the Bishop score, the evidence indicates that sonography could be useful in planning induction of labor, significantly reducing the need for cervical ripening agents. A more comprehensive method integrating both sonography and digital exam may be more appropriate.

Three-dimensional volumetric gray-scale uterine cervix histogram prediction of days to delivery in full term pregnancy

OBJECTIVE

Our aim was to figure out whether volumetric gray-scale histogram difference between anterior and posterior cervix can indicate the extent of cervical consistency.

METHODS

We collected data of 95 patients who were appropriate for vaginal delivery with 36th to 37th weeks of gestational age from September 2010 to October 2011 in the Department of Obstetrics and Gynecology, Korea University Ansan Hospital. Patients were excluded who had one of the followings: Cesarean section, labor induction, premature rupture of membrane. Thirty-four patients were finally enrolled. The patients underwent evaluation of the cervix through Bishop score, cervical length, cervical volume, three-dimensional (3D) cervical volumetric gray-scale histogram. The interval days from the cervix evaluation to the delivery day were counted. We compared to 3D cervical volumetric gray-scale histogram, Bishop score, cervical length, cervical volume with interval days from the evaluation of the cervix to the delivery.

RESULTS

Gray-scale histogram difference between anterior and posterior cervix was significantly correlated to days to delivery. Its correlation coefficient (R) was 0.500 (P = 0.003). The cervical length was significantly related to the days to delivery. The correlation coefficient (R) and P-value between them were 0.421 and 0.013. However, anterior lip histogram, posterior lip histogram, total cervical volume, Bishop score were not associated with days to delivery (P >0.05).

CONCLUSION

By using gray-scale histogram difference between anterior and posterior cervix and cervical length correlated with the days to delivery. These methods can be utilized to better help predict a cervical consistency.

Prediction of cesarean delivery using the fetal-pelvic index

OBJECTIVE

The purpose of this study was to estimate the usefulness of the fetal-pelvic index (FPI) in the prediction of cesarean delivery among nulliparous and women who undergo a trial of labor after cesarean delivery (TOLAC).

STUDY DESIGN

This prospective cohort study included subjects at 2 hospitals from the University of Pennsylvania Health system. The study sample included nulliparous women and women who attempted TOLAC, with nonanomalous pregnancies at ≥37 weeks of gestation in vertex presentation (n = 221 and 207, respectively). FPI score was calculated with the ultrasound-based fetal biometric measures that were performed within 2 weeks of delivery and x-ray pelvimetry that was performed within 48 hours of delivery. Multivariable logistic regression was used to develop a clinical predictive index for cesarean delivery, which included FPI and clinical factors, in nulliparous women or women who attempted TOLAC. The prediction models were tested for accuracy with the area under the receiver operating characteristics curve.

RESULTS

Higher FPI scores were associated with greater odds of cesarean delivery. A unit increase in FPI score increased the odds of cesarean delivery by 15% (adjusted odds ratio, 1.15; 95% confidence interval, 1.09-1.21) for nulliparous women and 15% for women who attempted TOLAC (adjusted odds ratio, 1.15; 95% confidence interval, 1.10-1.20) after adjustment for maternal age, race, medical risk factors, and labor method. Among nulliparous women, the receiver operating characteristics analysis estimated an area under the curve of 0.88, with positive and negative predictive values of 76% and 87%, respectively. Similar findings were observed in the subgroup of women who attempted TOLAC.

CONCLUSION

The FPI when combined with clinical risk factors can identify accurately women who are at a high risk for cesarean delivery.

Labor induction with prostaglandin E2: characteristics of response and prediction of failure

OBJECTIVE

To characterize the response to labor induction with prostaglandin E2 (PGE2) and to identify risk factors for induction failure.

METHODS

A prospective controlled study of women admitted for labor induction with PGE2. Maternal characteristics, Bishop score and sonographic cervical length were documented at admission. The change in cervical characteristics and the emergence of uterine contractions following each application of PGE2 were analyzed.

RESULTS

Of the 88 women who were included in the study, 19 (21.6%) failed to response to PGE2. The following factors were independently associated with induction failure: nulliparity (odds ratio [OR] = 5.9, 95% confidence interval (CI): 1.2-30.2), pre-pregnancy body mass index >25 kg/m2 (OR = 5.4, 95% CI: 1.1-26.5), Bishop score <4 (OR = 2.3, 95% CI: 1.05-14.4), cervical length <25 mm (OR = 0.2, 95% CI: 0.1-0.8) and the development of uterine contractions in response to the first application of PGE2 (OR = 0.4, 95% CI: 0.1-0.93). Overall, most women required only one (60.9%) or two (85.5%) applications of PGE2 to achieve successful induction. The number of applications of PGE2 required to achieve successful induction was related to parity and cervical status at presentation.

CONCLUSIONS

Overall, most women who eventually respond to PGE2 do so following the first two applications of PGE2, and the contribution of subsequent applications is relatively small and related to cervical status at admission.

A new objective scoring system for the prediction of successful induction of labour

A prospective study was done in 311 women undergoing induction of labour for the formulation of a new score, which will be more objective than the conventional Bishop's score. Pre-induction cervical assessment was done by the transvaginal sonographic parameters followed by the digital examination. Labour induction was successful in 79.09%. A new score was formulated using the parameters having independent association and weighting of individual components was given according to its regression coefficients. A new score with a maximum value of 13 was proposed. The best cut-off point for the new score in receiver operating characteristics curve was six with a sensitivity of 95.5% and specificity of 84.6%. The new score was found to have a better area under the curve than the conventional score.

[Adding parity to the Bishop score for term labor induction: a retrospective study]

OBJECTIVE

To evaluate the interest to add parity to the Bishop score before induction of labor by intravenous oxytocin.

PATIENTS AND METHODS

This retrospective cohort study compared cesarean section rate for induction failure by intravenous oxytocin in nulliparous and multiparous with modified Bishop score from 7 to 9. The modified Bishop score is calculated by adding 2 points to the Bishop score if the patient had a previous vaginal delivery and 0 point in nulliparous.

RESULTS

Over 2 years, 468 patients were included (201 nulliparous and 267 multiparous). Cesarean section rate for induction failure was higher for nulliparous with a modified Bishop score equal to 7 or varying between 7 and 9. These results confirm that parity is an important predicting factor of successful labor induction. In multiparous, cesarean section rates for induction failure were not significantly different with Bishop score or modified Bishop score equal to 7.

CONCLUSION

Adding 2 points for multiparity at the Bishop score did not increase cesarean for failure of labor induction with intravenous oxytocin with a modified Bishop score from 7 to 9.

Comparison between sonographic cervical length and Bishop score in preinduction cervical assessment: a randomized trial

OBJECTIVE

To compare sonographically measured cervical length with the Bishop score in determining the requirement for prostaglandin administration for preinduction cervical ripening in nulliparae at term.

METHODS

One hundred and fifty-four women with singleton pregnancies at term who were scheduled for induction of labor were randomly assigned to receive prostaglandin for preinduction cervical ripening based on the Bishop score or sonographic cervical length. A cervix unfavorable for treatment with prostaglandin for preinduction cervical ripening was defined as having either a Bishop score of ≤ 4 or a cervical length of ≥ 28 mm. The primary outcome measures were induction success (defined as an ability to achieve the active phase of labor) and the percentage of patients treated with prostaglandin for preinduction cervical ripening.

RESULTS

The two groups were similar with respect to maternal demographics, gestational age, cervical length, and Bishop score. The rates of induction success and Cesarean delivery, the interval to active phase of labor, and the interval to delivery were also similar in the two groups. However, in the transvaginal ultrasound group (n = 77), prostaglandin was administered to only 36% of the nulliparae compared with 75% of those in the Bishop score group (n = 77) (P < 0.0001).

CONCLUSION

In comparison with the Bishop score, the use of sonographic cervical length for assessing the cervix prior to induction of labor can reduce the need for prostaglandin administration by approximately 50% without adversely affecting the outcome of induction in nulliparae at term if the cut-off values used are a Bishop score of ≤ 4 and a cervical length of ≥ 28 mm.

Predictors of successful labor induction with oral or vaginal misoprostol

OBJECTIVE

To identify independent predictors of successful labor induction with oral or vaginal misoprostol.

METHODS

Women enrolled in four previous randomized trials involving oral or vaginal misoprostol for cervical ripening and labor induction were included in the present cohort study, with dosing of 25-50 microg every 4 to 6 h vaginally (n = 574) or 50 microg every 4 h orally (n = 207). Multiple logistic regression was performed to identify factors independently associated with successful labor induction -- defined as vaginal delivery within 12 h, vaginal delivery within 24 h and spontaneous vaginal delivery. Predictors of Cesarean birth and the need for only one dose of misoprostol were also identified. Variables included in the models were maternal age, weight, height, parity, gravidity, membrane status, route of misoprostol, gestational age, birth weight, and Bishop score and its individual components.

RESULTS

Maternal age, height, weight, parity, birth weight, dilatation, effacement and cervical station were associated with vaginal delivery within 24 h of induction. Maternal age, height, weight, nulliparity, birth weight and route of misoprostol were associated with Cesarean birth, with oral misoprostol being associated with a lower rate of Cesarean birth. The need for only one dose of misoprostol was predicted by maternal height, weight, parity, gestational age, Bishop score and route of misoprostol.

CONCLUSION

Characteristics of the woman (height, weight, parity), the fetus (birth weight) and some of the individual components of the Bishop score, were associated with successful labor induction, with oral misoprostol being associated with a lower rate of Cesarean birth.

The role of cervical Electrical Impedance Spectroscopy in the prediction of the course and outcome of induced labour

Background

Previous work by us and others had suggested that cervical electrical impedance spectroscopy (EIS) may be predictive of the outcome of induced labour. We sought to determine which probe configuration of the EIS device is predictive of the outcome of induced labour and compare this to digital assessment by the Bishop score.

Methods

In a prospective cohort of 205 women admitted for induction of labour, we used four probes of diameter 3, 6, 9 and 12 mm connected to an impedance meter to measure cervical resistivity (CR) in Ohm.meters at 14 electrical frequencies and compared their values to digital assessment of the cervix by the Bishop score for the prediction of the outcome of induced labour. We tested the association of labour characteristics and outcomes with CR and Bishop score by stepwise multilinear regression analyses, and the accuracy of prediction of categorical clinical outcomes by analysis of the area under the curves (AUC) of derived Receiver Operator Characteristic (ROC) curves.

Results

Of the four CR probe dimensions studied, only the 12 mm probe was predictive of any labour indices. In the frequency range 19 - 156 kHz, CR obtained with this probe was higher in women who delivered by caesarean section (CS) than those who delivered vaginally, and in labours lasting > 24 hrs. Cervical resistivity at 78.1 kHz best predicted vaginal delivery [optimal cut-off <2.25 Ohm.meter, AUC 0.66 (95% CI 0.59-0.72), sensitivity 71.0%, specificity 56.5%, LR+ 1.63, LR- 0.51, P < 0.01] and labour duration >24 hrs [optimal cut-off 2.27 Ω.m, AUC 0.65 (95% CI 0.58, 0.72), sensitivity 71%, specificity 59%, LR+ 1.72, LR- 0.50, P < 0.05]. In contrast digital assessment by the Bishop score neither predicted vaginal delivery nor the duration of labour. However, Bishop score predicted time to onset of labour > 12 hours and induction-delivery interval < 24 hrs [optimal cut-off ≤ 4, AUC 0.8 (95% CI 0.75, 0.86), sensitivity 77%, specificity 76%, LR+ 3.3, LR- 0.3, P < 0.05] whilst CR did not.

Conclusion

Cervical resistivity appears predictive of labour duration and delivery mode following induced labour. However the low predictive values obtained suggest that its current design proffers no immediate clinical utility.

Prediction of risk for cesarean delivery in term nulliparas: a comparison of neural network and multiple logistic regression models

OBJECTIVE

We sought to develop a neural network (NN) to predict the risk for cesarean delivery (CD) in term nulliparas.

STUDY DESIGN

Using software (BrainMaker for Windows, Version 3.0; California Scientific Software, Nevada City, CA), we trained an NN with 225 patients obtained by chart review and included for nulliparity, singleton vertex > 36 weeks' gestation, and reassuring fetal heart rate on admission. Training inputs included several maternal and fetal clinical variables. Two logistic regression (LR) models using 225 and 600 patients (LR225 and LR600, respectively) were developed. The NN and LR models were tested for prediction of CD in a set of 100 patients not used for development.

RESULTS

The NN, LR225, and LR600 correctly predicted 53%, 26%, and 32% of the patients with CD and 88%, 95%, and 95% of the patients with vaginal delivery, respectively.

CONCLUSION

Compared with LRs, the NN was slightly better in predicting CD and was similar for predicting vaginal delivery in nulliparas with term singletons.

Ultrasound assessment of fetal head-perineum distance before induction of labor

OBJECTIVES

To evaluate fetal head-perineum distance measured by ultrasound imaging as a predictive factor for induction of labor, and to compare this distance with maternal factors, the Bishop score and ultrasound measurements of cervical length, cervical angle and occiput position.

METHODS

The study included 275 women admitted for induction of labor. The fetal head-perineum distance was measured by transperineal ultrasound imaging as the shortest distance from the outer bony limit of the fetal skull to the skin surface of the perineum. Cervical length and angle was measured by transvaginal ultrasound examination, and fetal head position was assessed by transabdominal ultrasound imaging. The Bishop score was assessed without knowledge of ultrasound measurements. Receiver-operating characteristics (ROC) curves were used for evaluation of the probability of a successful vaginal delivery. The time from induction to delivery was tested using Cox regression analysis with ultrasound measurements, parity and body mass index (BMI) as possible predictive factors.

RESULTS

Areas under the ROC curve for prediction of vaginal delivery were 62% (95% CI, 52-71%) for fetal head-perineum distance (P = 0.03), 61% (95% CI, 51-71%) for cervical length (P = 0.03), 63% (95% CI, 52-74%) for cervical angle (P = 0.02), 61% (95% CI, 52-70%) for Bishop score (P = 0.03) and 60% (95% CI, 51-69%) for BMI (P = 0.05). The Cesarean delivery rate was 22% among nulliparous and 5% among parous women (P < 0.01). Parity, fetal head-perineum distance, cervical length and cervical angle were contributing factors predicting vaginal delivery within 24 h in a Cox regression model. Occiput posterior position had no significant predictive value.

CONCLUSIONS

Fetal head-perineum distance measured by transperineal ultrasound examination can predict vaginal delivery after induction of labor, with a predictive value similar to that of ultrasonographically measured cervical length and the Bishop score. However, we judge none of these methods used alone to be good enough in a clinical setting.

Pre-induction sonographic assessment of the cervix in the prediction of successful induction of labour in nulliparous women

OBJECTIVE

To compare the efficacy of ultrasonographic cervical assessment with Bishop score before induction of labour in predicting the success of labour induction in nulliparous women.

METHODS

This is a prospective study conducted in 138 women who underwent cervical assessment with transvaginal sonography followed by digital cervical assessment using Bishop score before induction of labour. Ultrasonographic parameters evaluated were cervical length, posterior cervical angle and funnelling were blinded to the managing physicians. Statistical analysis was carried out using Mann-Whitney test, chi2 test, receiver operating characteristics curves and logistic regression analysis.

RESULTS

Induction of labour was successful in 106 (76.8%) of the women. Multiple logistic regression analysis demonstrated cervical length and posterior cervical angle assessed by transvaginal sonography as independent predictors of successful outcome after induction of labour. Neither Bishop score nor its individual parameters were found to be significant in the regression analysis. The area under the receiver operating characteristic curve for cervical length and posterior cervical angle was greater than that of the Bishop score in predicting a successful labour induction. The best cut-off point for the parameters in receiver operating characteristics curve was 3.0 cm for cervical length and 100 degrees for posterior cervical angle. Cervical length of 3.0 cm had a sensitivity of 84.9%, and a specificity of 90.6% and a posterior cervical angle of 100 degrees with 65% and 72%, respectively.

CONCLUSIONS

Transvaginal sonographic assessment of cervical length and posterior cervical angle is better than conventional Bishop score in predicting successful labour induction in nulliparous women.

Sonographic cervical assessment to predict the success of labor induction: a systematic review with metaanalysis

OBJECTIVE

The purpose of this investigation was to review the literature that evaluates sonographic cervical assessment to predict successful induction of labor.

STUDY DESIGN

Published prospective trials that measured sonographic cervical length before labor induction was initiated were evaluated. Trials were excluded if they contained data presented in later articles or did not contain extractable data. The total analysis included 20 trials with 3101 aggregate participants.

RESULTS

Cervical length predicted successful induction (likelihood ratio of positive test, 1.66; 95% confidence interval [CI], 1.20-2.31) and failed induction (likelihood ratio of negative test, 0.51; 95% CI, 0.39-0.67). Cervical length did not predict any specific outcome (eg, mode of delivery). The assessment of cervical wedging proved to be a useful diagnostic test, with a likelihood ratio of a positive test result of 2.64 and a likelihood ratio of a negative test result of 0.64.

CONCLUSION

Sonographic cervical length was not an effective predictor of successful labor induction. Further evaluation of cervical wedging in the prediction of labor induction appears warranted.

Electrical impedance spectroscopy of the cervix in non-pregnant and pregnant women

OBJECTIVES

We sought to validate and measure the electrical impedance of the uterine cervix in non-pregnant and pregnant women by spectroscopy.

STUDY DESIGN

Cervical stromal impedance (CSI) was measured in 50 non-pregnant, 20 1st, 20 2nd and 50 3rd trimester pregnant women. The technique was also validated by comparing in vivo data to a finite element (FE) model of cervical tissue.

RESULTS

CSI agreed well with the FE model and was highly reproducible in all study groups. Mean (S.E.) CSI at 4-819 kHz was higher in pregnant (2.78 +/- 0.09 Omega m) compared to non-pregnant (2.38 +/- 0.07, p < 0.01) women, and in the 3rd trimester (3.08 +/- 0.13) compared to non-pregnant (p < 0.01), 1st trimester (2.42 +/- 0.12, p < 0.001) and 2nd trimester (2.20 +/- 0.05, p < 0.001) pregnant women.

CONCLUSION

Measurement of CSI provides a non-invasive method of assessing cervical tissue characteristics. Cervical extracellular matrix synthesis and leukocyte infiltration may account for the increased tissue impedance noted in the 3rd trimester.

Clinical and Ultrasound Parameters to Predict the Risk of Cesarean Delivery After Induction of Labor

OBJECTIVE

To evaluate whether factors in the maternal history and/or ultrasound parameters are useful in predicting the risk of cesarean delivery after induction of labor.

METHODS

Maternal age, height, body mass index, parity, gestational age, Bishop score, ultrasonic amniotic fluid volume, fetal head position, estimated fetal weight, and transvaginal cervical length were studied prospectively in 267 women at 36 or more weeks of gestation immediately before induction of labor. Logistic regression analysis was used to determine which factors best predicted the risk of cesarean delivery. Receiver operating characteristic curves and a resampling technique were used to evaluate the model's performance.

RESULTS

Eighty (30%) of these 267 women had cesarean delivery. Logistic regression was performed and a final model chosen, which included parity (odds ratio [OR] 20.56, 95% confidence interval [CI] 7.97-53.05, P < .001), body mass index (OR 6.17, 95% CI 2.10-18.13, P < .001), height (OR 0.94, 95% CI 0.89-0.98, P = .005), and ultrasonic transvaginal cervical length (OR 1.07, 95% CI 1.04-1.11, P < .001) as the best predictors of cesarean delivery. A risk score was calculated containing these 4 parameters, which predicted reasonably accurately the risk of cesarean delivery.

CONCLUSION

Parity, body mass index, height, and ultrasonic transvaginal cervical length are the most accurate parameters in predicting the risk of cesarean delivery after induction of labor. A predictive model using these would allow more accurate counseling and better informed consent in the decision-making process regarding induction of labor

LEVEL OF EVIDENCE

II-2.

Sonographic cervical length measurement before labor induction in term nulliparous women

OBJECTIVE

The purpose of the study was to determine if transvaginal sonographic measurement of the cervical length is a useful method to predict successful labor induction in nulliparas.

METHODS

137 women who were scheduled for medically indicated induction of labor had a transvaginal sonographic measurement of the cervical length before labor induction. Inclusion criteria were: (1) singleton pregnancy; (2) gestational age between 37-42 weeks; (3) live fetus in cephalic presentation; (4) intact membranes; (5) no vaginal bleeding; (6) no previous history of uterine surgery; (7) nulliparous women, and (8) no allergy or asthma in response to prostaglandins. Induction of labor was performed within 6 h of the ultrasonographic examination, by inserting 2 mg of dinoprostone in the posterior vaginal fornix, repeated if needed every 6 h for up to three doses. When the cervix became favorable and no regular contractions were observed, amniotomy and oxytocin augmentation, starting at 1 mIU/min and increasing 1 mIU every 30 min as necessary, was performed.

RESULTS

All women were Caucasians and the mean age was 24.3 years (range 19-37 years). The mean cervical length was 28 mm (range 11-39 mm). The Bishop score was < or =5 in 101 women and >5 in the 36 others. Vaginal delivery occurred in 92 women (67.1%), and the vast majority of them (89 women; 96.7%) gave birth within 24 h of induction. Forty-five women (32.8%) had a cesarean section. The Bishop score was not predictive of the mode of delivery. Thirty-six of 101 women (35.6%) with a Bishop score < or =5 delivered by cesarean section, compared to 9 of 36 women with a Bishop score >5 (25%) (p = NS). Women with a cervical length <27 mm were more likely to deliver vaginally. Using this cutoff value the sensitivity of a successful labor induction was 76% and the specificity was 75.5%.

CONCLUSIONS

Transvaginal sonographic measurement of cervical length is a good predictor of a successful labor induction at term in nulliparas.

Fetal Fibronectin as a Predictor of Vaginal Birth in Nulliparas Undergoing Preinduction Cervical Ripening

OBJECTIVE

We sought to evaluate whether the presence of a positive fetal fibronectin (> or = 50 ng/mL) in nulliparous women undergoing preinduction cervical ripening with the intracervical Foley catheter predicted vaginal birth.

METHODS

This was a prospective blinded observational trial of nulliparous women undergoing preinduction cervical ripening. We excluded women who had a contraindication to vaginal birth. Cervical and vaginal fetal fibronectin specimens were obtained before preinduction cervical ripening with an intracervical Foley catheter. The managing obstetrician was blinded to these results.

RESULTS

A total of 241 women met the inclusion criteria, of which 54.4% delivered vaginally. There was no difference in the rate of vaginal delivery among women with either a positive cervical fetal fibronectin (positive fetal fibronectin 55.8% compared with negative fetal fibronectin 53.3%, P = .70) or positive vaginal fetal fibronectin (positive fetal fibronectin 57.6% compared with negative fetal fibronectin 53.3%, P = .56). Women with a positive cervical fetal fibronectin did have a shorter duration of cervical ripening (fetal fibronectin-positive 229 +/- 220 minutes compared with fetal fibronectin-negative 379 +/- 193 minutes, P < .05), duration of oxytocin (fetal fibronectin-positive 655 +/- 555 minutes compared with fetal fibronectin-negative 731.5 +/- 342 minutes, P < .025) and required lower maximal doses of oxytocin (fetal fibronectin-positive 18.4 mIU/min compared with fetal fibronectin-negative 21.8 mIU/min, P = .005). Women with a positive vaginal fetal fibronectin demonstrated only a shorter duration of cervical ripening compared with their fetal fibronectin negative counterparts (fetal fibronectin-positive 300 +/- 216 minutes compared with fetal fibronectin-negative 345 +/- 201 minutes, P < .05).

CONCLUSION

Fetal fibronectin does not predict vaginal delivery in nulliparous women requiring preinduction cervical ripening.

LEVEL OF EVIDENCE

II-2.

Comparison of digital and ultrasonographic examination of the cervix in predicting time interval from induction to delivery in women with a low Bishop score

OBJECTIVE

To compare pre-induction ultrasonographic cervical length and Bishop score in predicting time to delivery after labour induction with prostaglandins.

DESIGN

Prognostic cohort study.

SETTING

Tertiary referral maternity unit in a teaching hospital.

POPULATION

Two hundred and sixty-six women with singleton pregnancies at between 34(+0) and 41(+3) weeks of gestation requiring induction of labour with prostaglandins for medical indications.

METHODS

A secondary analysis of a trial comparing two prostaglandins. Assessment of the Bishop score and measurement of the cervical length by transvaginal sonography were performed by two operators, blinded to each other's results. We estimated the predictive effects on the outcomes of ultrasonographic cervical length and Bishop score.

MAIN OUTCOME MEASURE

Time intervals from induction to delivery and to vaginal delivery.

RESULTS

Cervical length and Bishop score were associated with the time interval from induction to delivery, based on univariable analyses. When considered jointly in a multivariable model, only the Bishop score was significantly related to the outcome: The higher the Bishop score, the higher the hazard to delivery [hazard ratio (HR): 1.2, 95% confidence interval (CI): 1.1-1.3], illustrating that once the Bishop score is taken into account, further knowledge of cervical ultrasound length (HR: 0.99, 95% CI: 0.98-1.0) did not add any predictive information. Also, Bishop score was predictive of time interval between induction and vaginal delivery (HR: 1.2, 95% CI: 1.1-1.4) while cervical length had no additional predictive value (HR: 0.99, 95% CI: 0.98-1.0) when both cervical length and Bishop score were introduced in the model.

CONCLUSIONS

The Bishop score appears to be a better predictor of the time interval from induction to delivery and to vaginal delivery than cervical length after induction of labour for medical reasons.

Comparaison du score de Bishop et de la mesure échographique de la longueur du col dans la prédiction du risque de césarienne avant maturation du col par prostaglandines

OBJECTIVE

To compare pre-induction ultrasonographic cervical length and Bishop score in predicting risk of caesarean section after labor induction with prostaglandins.

PATIENTS AND METHODS

Assessment of the Bishop score and measurement of the cervical length by transvaginal sonography were performed by two operators, blinded to each other's results among women with singleton pregnancies at between 34(+0) - 41(+3) weeks of gestation requiring induction of labor with prostaglandins for medical indications. Fisher's exact test and regression logistic models were used for statistics analysis. In order to measure the strength of the association between ultrasonographic cervical length or Bishop score on one hand, and the caesarean sections rate (global or for failed induction or failure to progress) on the other hand, we computed odds ratios with 95% confidence interval.

RESULTS

Among the 266 patients included in the study, multivariate analysis has shown that only Bishop score was predictive for the global caesarean section risk (OR [95% CI] 0.63 [0.45-0.87] ; P =0.005). However, neither Bishop score (OR [95% CI] 0.68 [0.42-1.09] ; P =0.11), nor ultrasonographic cervical length (OR [95% CI] 1.01 [0.95-1.08] ; P =0.59) was predictive for failed induction or failure to progress caesarean section risk.

DISCUSSION AND CONCLUSION

The Bishop score appears to be a better predictor of the global caesarean section risk than ultrasonographic cervical length after induction of labor for medical reasons.

Reliability of the Bishop score before labour induction at term

OBJECTIVE

To evaluate the agreement within three pairs of observers regarding the Bishop score and an informal global evaluation of the cervix (favourable/unfavourable).

STUDY DESIGN

We conducted a reliability study of the Bishop score. Three pairs of examiners (A-B, A-C and D-E) performed independently a cervical examination in 156 term pregnant women admitted for labour induction. We calculated the proportion of agreement and the Kappa coefficient.

RESULTS

Perfect agreement between two observers for the Bishop score was found in 44 women (28%). Accepting a difference of one point between the observers, agreement increased to 66%. Weighted Kappa coefficients for the Bishop score were 69, 54 and 35% for each pair of observers. Kappa coefficients for the informal evaluation of the cervix were 64, 45 and 46, respectively.

CONCLUSION

Agreement between two observers evaluating the cervix is fair to substantial. An informal evaluation of the cervix is as reliable as the Bishop score.

The role of ultrasound and fetal fibronectin in predicting the length of induced labor when the cervix is unfavorable

OBJECTIVE

To compare cervical clinical data, ultrasound parameters and fetal fibronectin assessment in the prediction of the duration of induced labor when the cervix is unfavorable.

METHODS

This was a prospective study of 90 pregnant women with a Bishop score </= 5 undergoing labor induction. The Bishop score and its components, parity, cervical ultrasound parameters and fetal fibronectin level were analyzed using Cox's model in order to determine the most predictive factors for the duration of the latent and active phases of labor as well as its total duration.

RESULTS

There was a significant correlation between duration of the latent phase and the whole of labor, and digitally assessed cervical dilatation (P = 0.003 and P < 0.001, respectively), parity (P = 0.006 and P < 0.001), the Bishop score (P = 0.019 and P = 0.003) and ultrasound-determined cervical length (P = 0.035 and P = 0.003). The length of the active phase of labor did not correlate with the cervical status. Funneling did not appear to be predictive of the duration of labor and it had a poor correlation with digital cervical dilatation. The length of the latent phase and that of the whole of labor was significantly longer when cervical dilatation was </= 2 cm (P < 0.001 in each case), when women were nulliparous (P = 0.002 and P < 0.001) and when ultrasound cervical length was >/= 27 mm (P = 0.002 and P = 0.005).

CONCLUSION

Cervical dilatation as assessed by digital examination is the best predictor of the duration of the latent phase and of that of the whole of labor. Ultrasound measurement of cervical length is not more accurate at predicting the duration of labor than are clinical data.

Does ultrasound examination when the cervix is unfavorable improve the prediction of failed labor induction?

OBJECTIVE

To compare the Bishop score, ultrasound cervical parameters and fetal fibronectin assessment for predicting failed labor induction when the cervix is unfavorable.

METHOD

A prospective observational study was performed in 106 consecutive pregnant women with a Bishop score < or =5 undergoing labor induction. Assessment of fetal fibronectin and ultrasound measurement of cervical length, cervical wedging and cervical lip areas were performed. The relationship between these parameters and failure of labor induction was determined.

RESULTS

Failure of labor induction was defined as failure to reach a cervical dilatation of > or =5 cm, and it occurred in 16 patients (15.1%). Induction failure was associated with low Bishop scores before (P = 0.004) and 6 h after the start of induction (P = 0.007), increased clinical cervical length (P = 0.02) and increased ultrasound anterior cervical lip area (P = 0.04). The logistic regression model identified the Bishop score before induction (odds ratio = 2.25; 95% CI, 1.30-3.91; P = 0.003) and the clinical cervical length (odds ratio = 3.95; 95% CI, 1.3-11.7; P = 0.01) as being independent predictors of failed induction. To predict an induction failure, the best Bishop score cut-off value was 4, with a sensitivity of 87.5%, a specificity of 45.6%, a likelihood ratio of 1.58, a positive predictive value of 22.2% and a negative predictive value of 95.4%.

CONCLUSION

Compared with the Bishop score, cervical length by ultrasound is not a better predictor for the outcome of labor induction in an unfavorable cervix. Nevertheless, the Bishop score appears to be of poor predictive value for failed induction of labor.

Transvaginal ultrasonography for cervical assessment before induction of labor

OBJECTIVE

To evaluate the value of ultrasonographic cervical assessment in predicting the outcome of labor induction and to compare its performance against the Bishop score.

METHODS

The Bishop score was determined by digital examination, and transvaginal ultrasonography was performed in 105 women at 37 to 42 weeks' gestation scheduled for labor induction. Ultrasonographic parameters evaluated were cervical length, the presence of funneling, funnel width, and funnel length and were blinded to managing physicians. The primary outcome was the occurrence of active labor within 2 days (successful labor induction). The interval from the onset of induction to active labor (duration of induction) was the secondary outcome. Statistical analysis was performed by the chi2 test, Wilcoxon rank sum test, Pearson correlation, receiver operating characteristic curves, logistic regression, Cox proportional hazards model, and generalized Wilcoxon test for survival data.

RESULTS

Induction of labor was successful in 93 women (89%). The area under the receiver operating characteristic curve for cervical length was greater than that of the Bishop score in predicting a successful labor induction (z = 2.18; P < .05). A cervical length of 3.0 cm or less had sensitivity of 75% (70 of 93) and specificity of 83% (10 of 12). Multiple logistic regression analysis showed a significant relationship between successful labor induction and cervical length but not the Bishop score (odds ratio = 0.24; 95% confidence interval, 0.096-0.59; P = .002). Only parity and cervical length had a significantly independent relationship with the duration of induction.

CONCLUSIONS

Cervical length measured by transvaginal ultrasonography is a useful and independent predictor of successful labor induction and the duration of induction and provides better predictability of successful labor induction than the Bishop score does.

Quantitative foetal fibronectin as a predictor of successful induction of labour in post-date pregnancies

OBJECTIVE

To study the relationship between induced labour, quantitative levels of fibronectin and the Bishop score.

STUDY DESIGN

Vaginal fibronectin/Bishop score were estimated in 33 nulliparous women undergoing induction of labour for post-dates at the Department of Obstetrics and Gynaecology, Guy's and St. Thomas' Hospital London.

RESULTS

There was no significant relationship between either the fibronectin level or Bishop score and the duration of the latent phase (R(2)=0.001; P=0.86 and R(2)=0.12; P=0.08, respectively). There was no relationship between the total prostaglandin dose and fibronectin level (R(2)=0.03; P=0.39) nor any significant correlation between either the Bishop score or fibronectin level and the induction to delivery time (R(2)=0.13; P=0.11 and R(2)=0.0006; P=0.97, respectively). Significant relationships were observed inversely between the total prostin dose and Bishop score (R(2)=0.33; P=0.002), between the total prostin dose and latent phase (R(2)=0.54; P=0.000009) and between Bishop score and the fibronectin levels (R(2)=0.19; P<0.01).

CONCLUSIONS

Quantitative foetal fibronectin is not a useful test for inducibility at term.

Transvaginal sonography of the uterine cervix prior to labor induction

OBJECTIVES

To compare the Bishop score and transvaginal sonographic measurement of cervical length for predicting the mode of delivery following medically indicated induction of labor in term patients.

METHODS

The study was conducted prospectively in 179 women who required medically indicated induction of labor. Inclusion criteria were singleton pregnancy, gestational age > 37 weeks of amenorrhea, cephalic presentation and intact fetal membranes. Cervical length was measured upon arrival in the labor room but was not considered when choosing the induction procedure. Two receiver-operating characteristic curves were plotted to calculate the best threshold value for the Bishop score and for cervical length for predicting the risk of Cesarean section.

RESULTS

Fifty-three women (29.6%) had a Cesarean section. The Bishop score was not predictive of the delivery mode, although Cesarean section for failure to progress was more frequent when the Bishop score was < or = 5. Among the women with a Bishop score > 5, the cervical length was not predictive of the induction outcome. However, among the women with a Bishop score < or = 5, a cervical length < 26 mm was associated with a lower Cesarean section rate (20.6 vs. 42.9%; P = 0.006). Furthermore, the interval between the beginning of cervical ripening and delivery was shorter in the case of a short cervix (11.01 +/- 6.7 vs. 18.55 +/- 7.07 h; P < 10(-5)).

CONCLUSION

The length of the uterine cervix, measured by transvaginal sonography, is a better predictor of the risk of Cesarean section than the Bishop score after induction of labor for medical reasons. In women with an unfavorable Bishop score, a cervical length of < 26 mm is associated with a lower risk of Cesarean section and a shorter duration of labor.

Reducing the caesarean delivery risk in elective inductions of labour: a decision analysis

To determine whether the vaginal delivery rate is increased in nulliparous women who have positive fetal fibronectin (fFN) testing before elective induction of labour, we performed a decision analysis that tested three options: (1) spontaneous labour; (2) testing nulliparous candidates for elective induction of labour at 39 weeks gestation with fFN and inducing labour if fFN positive (women who are fFN negative are managed expectantly); (3) elective induction of labour for women who are at least 39 weeks. We found that spontaneous labour had a vaginal delivery rate of 90, elective induction 79 and fFN screening 83. At baseline, a mother must be willing to take an additional 7 risk of caesarean delivery to warrant fFN testing or an additional 11 risk of caesarean delivery to warrant elective induction. We conclude that spontaneous labour has the highest vaginal delivery rates. An fFN test in a nulliparous woman may help to raise her likelihood of a vaginal delivery in an elective induction.