Ginekologia i Poloznictwo
ISSN 1896-3315 e-ISSN 1898-0759

Cervical Length and Posterior-Cervical Angle in Prediction of Successful Induction of Labor

Sabry Sayed Mohamed Hassan, Ahmed Elsayed Ahmed Omar^*, Ahmed Mohamed Essam and El-Din Mahmoud Mansour ^*Correspondence: Ahmed Elsayed Ahmed Omar, Department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University, Cairo, Egypt, Tel: +201019391381, Email:

Received: 03-Sep-2021 Published: 28-Dec-2021

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Introduction

Induction of labor (IOL) is a popular obstetrical procedure, accounting for about 20–30% of all deliveries [1]. In women with an unripe cervix, IOL helps to avoid possible complications for the mother and the fetus [2].

Although following IOL, vaginal delivery (VD) is expected, complications may hinder the delivery, and the labor may fail to progress, which is defined as an unsuccessful IOL; accordingly, cesarean section (CS) is the alternative option. Low Bishop score (<6), maternal obesity, nulliparity, and gestation age < 41 weeks; are all considered as possible causes of unsuccessful IOL [3].

In clinical practice, the Bishop score [4] is the most commonly used way to evaluate the cervical condition [5]. However, some investigators concluded that Bishop score is a flawed method for predicting the success of IOL due to the imprecise nature of cervical assessment. Bishop score faces difficulties in evaluating the internal os changes, especially while the external os is closed. In addition, this is considered a subjective measurement influenced by the clinical experience of the physician [6].

Transvaginal ultrasound (TVUS) parameters have been shown superiority over the conventional Bishop score in evaluating the cervix before IOL. This superiority is explained by the reproducibility of TVUS data and learning feasibility [7]. Cervical length (CL) and posterior-cervical angle (PCA) are two ultrasound parameters that have been identified to evaluate the clinical functionality of the cervix that assess the quality of cervical integrity [8].

This study aimed to assess the reliability of measuring both PCA and CL using TVUS compared with Bishop score to predict the success of IOL.

Materials and Methods

Study design: A prospective observational study (Accuracy of diagnostic test study) was carried out on 100 pregnant women admitted for IOL at Ain Shams University Maternity Hospital during the period from October 2019 to October 2020. The study scheme is simplified in supplementary Figure 1 in the addendum.

Study population: All women included in the study were primigravida, with one live fetus in cephalic presentation. The candidates were not in active labor which is defined as (cervical dilatation > 4-cm or cervical effacement > 80 %) [9]. However, all pregnant women with confirmed fetal anomalies, amniotic fluid disorders, Bishop score > 8, antepartum hemorrhage, cephalopelvic disproportion, previous cervical operation, previous cesarean delivery and myomectomy (previous uterine scar), and those who are morbidly obese (Body Mass Index (BMI) over 40 calculated as weight in kilograms divided by square of height in meters), fetal macrosomia (fetal weight 4 kg or more measured by ultrasonography), fetal distress, or uterine anomalies were excluded from the study.

Ethical approval: The study was presented for approval from the Ethical Committee of the Department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University. Informed consent was received from all participants after counseling them on the nature of the study.

Methods

All women were subjected to full history taking, physical examination, ultrasonography examination by two ultrasound experts;

a) Abdominal ultrasound was done by Samsung (Seoul, South Korea) ultrasound system by frequency 7 MHZ to determine fetal viability, weight, number, amniotic fluid, and placental site.

b) Transvaginal ultrasound (TVUS) was performed with an empty bladder in the lithotomy position with a frequency 4 -9 MHZ by Samsung (Seoul, South Korea) ultrasonography machine. Gently, the vaginal probe was introduced into the vagina till the back of the fornix was reached to see the whole cervical length. A sagittal cervix plane has been obtained, ensuring proper visualization of the full length of the cervical canal. The calipers were put between both the inner and outer cervical openings for the CL measurement. We measured the angle between the line used in measuring the CL and the back of the uterine wall for the PCA measurement [10]. Finally, to calculate the Bishop score, a digital examination was done [11]. Measurements of both CL and PCA were kept blinded from the investigator who performed the Bishop scoring.

Induction of Labor: The protocol for IOL followed the local university hospital protocol. We gave cervical ripening agents in the form of a vaginal tablet containing 25 μg misoprostol (Vagiprost; Adwia, Cairo, Egypt) to those with a firm or closed cervix to be repeated at least after 4 hours up to 5 doses. In comparison, women with a flexible cervix and others improved by misoprostol were given an intravenous oxytocin infusion (Syntocinon; Novartis, Basel, Switzerland). The initial dosage was 5 units (in 500 ml Ringer solution), an average of 12 drops per minute. Each half an hour, we doubled the dosage till we reach effective constrictions, the maximum dose up to 96 drops per minute.

We compared the measured PCA and CL with bishop score for evaluation of successful IOL that was defined as the time interval for induction to active labor (according to ACOG [9] where cervical dilatation >4-cm or cervical effacement > 80 %). In comparison, unsuccessful IOL was defined as cesarean delivery because of failed progress of labor. Women who had a cesarean delivery for reasons other than failed IOL, such as prepartum hemorrhage, fetal distress, and cephalopelvic disproportion, were excluded from the data analysis.

Statistical analysis of the data: Data were fed to the computer using IBM SPSS software package version 20.0. Qualitative data were described using numbers and percent [12]. Detailed information is explained in the supplementary materials (addendum).

Results

The present study included 100 pregnant women aged 18-39 years with gestational age from 37-41 weeks. Demographic, clinical, and ultrasonography characteristics of the study group are illustrated in Table 1.

Tab. 1. Demographic, clinical, and ultrasonography characteristics of study group.

Regarding induction of Labor, unsuccessful IOL was recorded in 17 women (17%), including eight women (8%) with fetal distress and nine women (9%) with failed IOL. Whereas successful IOL was reported in 83 women (83%). Regarding mode of delivery, 83 women (83%) were delivered via spontaneous vaginal delivery (SVD), and 17 (17%) were delivered via lower segment Cesarian section (LSCS).

In the current study, induction time ranged from 4-18 hours with a mean value of 8.44 ± 3.15 hours and induction to delivery time ranged from 6-24 hours with a mean value of 12.16 ± 4.06 hours. The time from induction to delivery was < 24 hrs in 79 women (95.2%) and > 24 hrs in 4 women (4.8%).

Bishop score, CL, and PCA values in women with failed and successful IOL are shown in Tab. 1. A significant statistical difference was recorded between failed versus successful induction outcomes concerning Bishop score, CL, and PCA (P < 0.001*) (Tab. 1.).

ROC curves of Bishop score, CL, and PCA for predicting successful IOL were performed. The AUC of PCA was the highest (AUC 0.905, 95% CI 0.80 – 0.96). Also, PCA showed the greatest sensitivity, specificity, and accuracy as it was 92.0, 89.0, and 89.0, respectively (Tab. 2.).

Tab. 2. Sensitivity, specificity, and accuracy of Bishop score, CL, PCL, (CL and PCA), (Bishop score and CL), and (Bishop score and PCA) to predict successful IOL.

ROC curves for combined CL and PCA, combined Bishop score and CL, and combined Bishop score and PCA were performed to predict successful IOL. The best prognostic combination was CL and PCA, showing a sensitivity of 94.0, specificity of 91.0, and accuracy of 91.0 (Tab. 2.).

Discussion

IOL is indicated when labor is more beneficial than waiting for spontaneous labor [2]. Bishop score was introduced in practice as a predictor of successful IOL, and it is considered one of the most critical and valuable scoring systems [13]. However, as alternatives for the conventional Bishop score, some ultrasound parameters are recommended particularly, CL and PCA [14].

In the current study, PCA and the CL measurements were assessed using TVUS in comparison with the Bishop score to predict the effectiveness of IOL.

This study was conducted at Ain Shams University Maternity Hospital on 100 pregnant women admitted for IOL, aged from 18-39 years, with a mean of 24.17 ± 3.94 and with a gestational age of 37-41 weeks.

In this study, IOL failed in 17 cases (17%), out of which 8 cases (8%) had fetal distress. After IOL, 83 cases (83%) delivered via SVD, while 17 cases (17%) were delivered by LSCS.

Jing's study included 475 cases indicated for IOL. Out of all cases, 393 (82.7%) delivered vaginally, and 82 (17.3%) had CS. Forty women failed to access the active phase of labor, 20 had fetal hypoxia, additionally to other different causes [15].

That vaginal dose of 50-μ5 of misoprostol was studied widely. Results demonstrated that such dose is more effective but not secure, unlike a 25-μg dosage [16]. In the present study, up to five tablets of 25-μg misoprostol tablets were used in the failed cases. While the successful cases used from 1-4 tablets.

As the cervical status before labor was identified as the most significant indicator of successful IOL, several studies have assessed the relation between the Bishop score and sonographic cervical measurement with IOL consequence [17,18].

In the current study, CL in failed IOL cases ranged from 29-37 with a mean value of 34.67 ± 2.40 while successful IOL cases ranged from 21-37 with a mean value of 28.76 ± 3.93. For the prediction of successful IOL at cut-off 34 mm, the CL showed sensitivity, specificity, and accuracy of 91.0, 83.0, and 86.0, respectively, with PPV of 86.0 and NPV of 80.0.

The meta-analysis of Verhoeven's study involved 31 analyses that reported both CL and delivery outcome. For cesarean deliveries, summary estimates of both sensitivity/specificity for CL were 0.82/0.34, 0.64/0.74, and 0.13/0.95 for different cut-offs 20, 30, and 40 mm, respectively. They concluded that CL and cervical wedging by TVUS at or near term could predict the outcome of delivery after IOL [5].

The Anikwe Study [18] reported that the mean induction delivery time for all participants was 8.1 ± 3.0 hours and a mean labor duration of 7.4 ± 2.9 hours. Pre-induction CL is a good predictor of a short labor duration (P = 0.001).

In the present study, Bishop score ranged from 2-4 with a mean value of 3.11 ± 0.93 in failed cases, while in successful cases ranged from 3-8 with a mean value of 5.64 ± 1.14. For the prediction of successful IOL, Bishop score at the cut-off point 5 demonstrated sensitivity, specificity, and accuracy of 90.0, 88.0, and 89.0, respectively, with PPV of 91.0 and NPV of 87.0. Thus, our study showed that the CL has better sensitivity, specificity, and accuracy in predicting successful IOL over Bishop score.

Kolkman's study [19] concluded that the Bishop score seems to be a weak predictor for IOL. In Bajpai's study [20] on 131 women who underwent IOL at term live fetuses, successful IOL was in 86.9% of patients. At cut-off values of ≥ 4, TVUS cervical parameters were better than Bishop score (Sensitivity 77% vs. 65%, Specificity 93% vs. 86%) in predicting successful IOL. ROC analysis illustrated that AUC was higher for TVUS Score (0.90, 95% CI 0.84 – 0.95) compared to Bishop score. Also, Kanwar's [21] concluded that within 24 hours of IOL, CL is a powerful predictor of vaginal delivery in comparison to the modified Bishop score.

On the contrary to our results, Khandelwal's study [22] on 62 nulliparous women who underwent IOL reported that the Bishop score had a higher significance (P-value < 0.0001) than CL (P = 0.004) in predicting the active phase of labor. Regarding Bishop score, the optimum cut-off point for predicting IOL through 6 hours was > 4, with a sensitivity of 69% and specificity of 79%. At the same time, the best CL's cut-off point for IOL prediction in 6 hours was < 25 mm by 51% sensitivity and 70% specificity. In addition, for predicting induction-to-delivery interval within 12 h, Bishop scores (P = 0.001) were also superior to CL (P = 0.01). Also, Bahadori [23] found a more significant correlation of Bishop (0.001) than of CL (0.04) for predicting cervical ripening within 12 hours. The cut-off value for Bishop score was ≥4, with a sensitivity and specificity of 57.9% and 28.7%, respectively, whereas the cut-off value for CL ≥19 mm had a sensitivity and a specificity of 66.7% and 65%, respectively.

In the current study, PCA in failed IOL cases ranged from 78-110 with a mean value of 91.56 ± 9.96 and in success IOL cases ranged from 70-150 with a mean value of 108.35 ± 17.94. To predict the success of IOL at a cut-off value of 99.0, PCA presented sensitivity, specificity, and accuracy of 92, 89.0, and 89.0, respectively, with PPV of 90 and NPV of 88. In addition, PCA showed a significant negative correlation with induction time, induction to delivery, and Vagiprost.

PCA > 99.5°, CL < 34 mm, and a Bishop score > 5 were suggested as cut-offs for the prediction of successful IOL by Al‐Adwy [24]. There was no significant difference among the AUC of those three measurements. However, the PCA > 99.5° had the highest sensitivity (91.84%), specificity (90.48), PPV (95.7%), and NPV (82.6%) comparing to the other two indicators.

The study conducted by Gokturk that included multi-variate regression analyses of variables showed that multiparity, CL, PCA, and Bishop score are good predictors for successful IOL [25].

Concerning the combination between parameters in our study, the combined CL and post PCA sensitivity, specificity, and accuracy to predict successful induction were 94.0, 91.0, 91.0, respectively. While Bishop score and CL sensitivity, specificity, and accuracy for predicting the success of induction were 90.0, 88.0, 89, respectively. In addition, the Bishop score and PCA’s sensitivity, specificity, and accuracy for the prediction of successful induction were 92.0, 89.0, and 90, respectively.

Overall, PCA showed the best sensitivity and specificity as an indicator for IOL outcome, especially in combination with CL measurement.

Conclusion

Our data concluded that ultrasonographic cervical assessment and Bishop score are good indicators of successful IOL. Still, sonographic parameters including CL and PCA seemed to be better than the Bishop score in predicting the outcome of labor induction, especially when used combined.

Acknowledgments

The authors of this study possess no acknowledgments to make with regards to this study and this manuscript’s content.

Declarations

The authors report no conflict of interest.

Funding

None.

References

1. Marconi AM. Recent advances in the induction of labor. F1000Research. 2019;8.
2. De Vivo V, Carbone L, Saccone G, et al. Early amniotomy after cervical ripening for induction of labor: a systematic review and meta-analysis of randomized controlled trials. Am J Obstet Gynecol. 2020;222(4):320-29.
3. Parkes I, Kabiri D, Hants Y, et al. The indication for induction of labor impacts the risk of cesarean delivery. J Matern Fetal Neonatal Med. 2016;29(2):224-8.
4. Bishop EH. Pelvic scoring for elective induction. Obstet Gynecol. 1964;24:266-8.
5. Verhoeven CJ, Opmeer BC, Oei SG, et al. Transvaginal sonographic assessment of cervical length and wedging for predicting outcome of labor induction at term: a systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2013;42(5):500-8.
6. Navve D, Orenstein N, Ribak R, et al. Is the Bishop-score significant in predicting the success of labor induction in multiparous women? J Perinatol. 2017;37(5):480-83.
7. Vayssière C, Morinière C, Camus E, et al. Measuring cervical length with ultrasound: evaluation of the procedures and duration of a learning method. Ultrasound Obstet Gynecol. 2002;20(6):575-9.
8. Myers KM, Feltovich H, Mazza E, et al. The mechanical role of the cervix in pregnancy. J Biomech. 2015 Jun 25;48(9):1511-23.
9. Neal JL, Lowe NK, Ahijevych KL, et al. “Active labor” duration and dilation rates among low-risk, nulliparous women with spontaneous labor onset: a systematic review. J Midwifery Womens Health. 2010;55(4):308-318.
10. Gokturk U, Cavkaytar S, Danısman N. Can measurement of cervical length, fetal head position and posterior cervical angle be an alternative method to Bishop score in the prediction of successful labor induction? J Matern Fetal Neonatal Med. 2015;28(11):1360-1365.
11. ACoPB. (ACOG Committee on Practice Bulletins -- Obstetrics). ACOG practice bulletin no. 107: induction of labor. Obstet Gynecol. 2009;114:386-97.
12. IBM Corp.  IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.
13. Ivars J, Garabedian C, Devos P, et al. Simplified Bishop score including parity predicts successful induction of labor. Eur J Obstet Gynecol Reprod Biol. 2016;203:309-14.
14. Papillon-Smith J, Abenhaim HA. The role of sonographic cervical length in labor induction at term. J Clin Ultrasound. 2015;43(1):7-16.
15. Lu J, Cheng YKY, Ho SYS, et al. The predictive value of cervical shear wave elastography in the outcome of labor induction. Acta Obstet Gynecol Scand. 2020;99(1):59-68.
16. McMaster K, Sanchez-Ramos L, Kaunitz AM. Balancing the efficacy and safety of misoprostol: a meta-analysis comparing 25 versus 50 micrograms of intravaginal misoprostol for the induction of labour. BJOG: Int J Obstet Gynaecol. 2015;122(4):468-76.
17. Baños N, Migliorelli F, Posadas E, et al. Definition of Failed Induction of Labor and Its Predictive Factors: Two Unsolved Issues of an Everyday Clinical Situation. Fetal Diagn Ther. 2015;38(3):161-9.
18. Anikwe CC, Okorochukwu BC, Uchendu E, et al. The Effect of Ultrasound-Measured Preinduction Cervical Length on Delivery Outcome in a Low-Resource Setting. Sci World J. 2020;2020:8273154.
19. Kolkman DG, Verhoeven CJ, Brinkhorst SJ, et al. The Bishop score as a predictor of labor induction success: a systematic review. Am J Perinatol. 2013;30(8):625-30.
20. Bajpai N, Bhakta R, Kumar P, et al. Manipal Cervical Scoring System by Transvaginal Ultrasound in Predicting Successful Labour Induction. J Clin Diagn Res. 2015 May;9(5):Qc04-9.
21. Kanwar SN, Reena P, Priya BK. A comparative study of trans vaginal sonography and modified Bishop score for cervical assessment before induction of labour. Sch J App Med Sci. 2015;3(6B):2284-8.
22. Khandelwal R, Patel P, Pitre D, et al. Comparison of Cervical Length Measured by Transvaginal Ultrasonography and Bishop Score in Predicting Response to Labor Induction. J Obstet Gynaecol India. 2018;68(1):51-57.
23. Bahadori F, Ayatollahi H, Naghavi-Behzad M, et al. Predicting factors on cervical ripening and response to induction in women pregnant over 37 weeks. Med Ultrason. 2013;15(3):191-8.
24. Al-Adwy AM, Sobh SM, Belal DS, et al. Diagnostic accuracy of posterior cervical angle and cervical length in the prediction of successful induction of labor. Int J Gynaecol Obstet. 2018;141(1):102-07.
25. Gokturk U, Cavkaytar S, Danısman N. Can measurement of cervical length, fetal head position and posterior cervical angle be an alternative method to Bishop score in the prediction of successful labor induction? J Matern-fetal Neo M. 2015;28(11):1360-65.