Utility of the Simplified Bishop Score in Trial of Labor After Cesarean Success
October 1, 2022
By Ahizechukwu C. Eke, MD, PhD, MPH
Associate Professor in Maternal Fetal Medicine, Division of Maternal Fetal Medicine, Department of Gynecology & Obstetrics, Johns Hopkins University School of Medicine, Baltimore
SYNOPSIS: This study demonstrated that a higher likelihood of vaginal birth after cesarean was associated with a favorable simplified Bishop score on admission. This emphasizes the need for delaying patient counseling on the choice of trial of labor after cesarean delivery until the end of pregnancy to incorporate the cervical exam into decision-making.
SOURCE: Oakes MC, et al. Simplifying the prediction of vaginal birth after cesarean delivery: Role of the cervical exam. J Matern Fetal Neonatal Med 2022; Jun 20:1-6. doi: 10.1080/14767058.2022.2086795. [Online ahead of print].
Over the past five decades, the rate of cesarean deliveries in the United States has progressively increased to the point that one in three women now have a cesarean delivery.1 As a result of the continued rise in the national cesarean delivery rate, clinical guidelines have recommended trial of labor after cesarean (TOLAC) delivery as a way to lower repeat cesarean deliveries.1 However, the safety and appropriateness of TOLAC have been questioned because of worries about maternal and perinatal morbidity linked to uterine rupture, a complication of TOLAC.1,2 At present, most practitioners would limit TOLAC to women with one or two prior lower segment cesarean deliveries, since data from meta-analyses have demonstrated that women who have had several prior cesarean deliveries face a nearly threefold higher risk of uterine rupture when compared to those with one previous cesarean delivery (1.59% vs. 0.72%).3
An independent variable linked to successful TOLAC is the Bishop score.4 A simplified Bishop score (SBS), consisting of three components, has been demonstrated to compare favorably with the original Bishop score for predicting successful vaginal delivery.5 However, an SBS that incorporates assessments of cervical station, dilatation, and effacement has never been used to predict the probability of successful TOLAC.6 In this manuscript, Oakes and colleagues assessed the association between admission SBS and the possibility of a successful vaginal birth after cesarean (VBAC), including assessing the advantages of SBS over cervical dilatation alone in predicting successful VBAC.6
This was a secondary analysis of a prospective cohort study of patients with singleton pregnancies ≥ 37 0/7 weeks’ gestation admitted for either an induction of labor or spontaneous labor at the Washington University School of Medicine between 2010 and 2014. Patients who had at least one prior cesarean delivery, were admitted for a TOLAC, and had a recorded admission SBS were included in the study. Patients with a reported previous classical cesarean delivery, known fetal abnormalities, three or more cesarean deliveries, or a fetal demise were excluded. Based on each patient’s cervical dilatation, effacement, and fetal position measurements at the time of admission, the SBS was determined. According to the criteria laid out by Laughon et al, a score of > 5 was judged good and a score of 5 was undesirable for TOLAC.5
The primary outcome measure was a successful VBAC, which was characterized as either a natural or operative vaginal delivery. Secondary outcomes were umbilical artery gas pH < 7, neonatal intensive care unit admission, uterine rupture, blood transfusion, chorioamnionitis, endomyometritis, third- or fourth-degree perineal lacerations, and five-minute Apgar score < 7. Demographics and outcome variables were analyzed using standard statistical tests. Multivariable regression models accounting for potential confounders were created for the primary and secondary outcomes with relative risks (RR) as the measures of effect. The Mantel-Haenszel test of homogeneity was used to stratify the cohort and examine the effects of prior cesarean deliveries (one vs. two), prior vaginal deliveries, and spontaneous vs. induction of labor on the likelihood of a successful VBAC. Using receiver-operating characteristic (ROC) curves, the authors contrasted the ability of cervical dilatation alone compared to SBS for VBAC prediction. The Youden index was used to identify the “optimal” cut-off values on the ROC curves.
A total of 8,580 participants who delivered during the study period were screened, and 656 (7.6%) who were admitted for TOLAC met the inclusion criteria. Of the patients who underwent a TOLAC, 203 (31%) had a favorable admission SBS, while 453 (69%) did not. Body mass index was higher in patients with a poor SBS compared to those with a good SBS (34.2 kg/m2 vs. 32.6 kg/m2, P = 0.01). There were no statistically significant differences between the two groups regarding maternal age, insurance status, maternal comorbidities, and proportion of favorable or unfavorable admission SBS among patients who had any prior vaginal delivery (spontaneous vaginal delivery or VBAC). A successful VBAC was experienced by 421 (64.2%) of the cohort’s 656 patients, while 235 (35.7%) of the patients ultimately underwent an intrapartum repeat cesarean delivery. Non-reassuring fetal heart tones was the most frequent reason for an intrapartum repeat cesarean delivery during a TOLAC (110/235, 46.8%), followed by labor arrest (76/235, 32.3%). Those who had a favorable admission SBS had a successful VBAC at a rate of 76.8% (156/203) as opposed to 58.5% (265/453) of patients who had an unfavorable SBS (RR, 1.31; 95% confidence interval [CI], 1.18-1.46). The “ideal” cut-off value for predicting VBAC was an SBS of 3.5 and cervical dilatation of 3.0 cm based on the maximum Youden index. Cervical dilatation alone had a comparable positive predictive value for successful VBAC as admission SBS (75.1%; 95% CI, 70.4-79.4 vs. 75.6%; 95% CI, 72.4-78.5, respectively).
There are several maternal and fetal risks associated with uterine rupture in women undergoing TOLAC. Hypoxic-ischemic encephalopathy, hysterectomy, cerebral palsy, and maternal and fetal death are among the most severe complications of uterine rupture in the setting of TOLAC.1,2 These risks are most deleterious in women who need a repeat cesarean delivery after attempting TOLAC. In women undergoing TOLAC, a history of previous vaginal delivery, either before or after a prior cesarean delivery, is a good predictive factor for possible successful TOLAC, and appears to reduce the risk of uterine rupture.7 The rate of uterine rupture during a TOLAC was 1.1% in pregnant women who had not previously given birth vaginally compared to 0.2% in pregnant women who had a prior vaginal delivery.8 Absolute contraindications to attempting TOLAC include prior history of classical cesarean delivery, previous inverted T or J uterine incision, a history of three or more prior low transverse cesarean deliveries, complete placenta previa, and a history of trans-fundal myomectomy. During prenatal care, it is pertinent to rule out placenta accreta spectrum disorders (PASD) in women with a history of prior cesarean delivery and placenta previa, since the risk of PASD increases with the number of previous cesarean deliveries.9
While spontaneous onset of labor is preferable in women with a history of previous cesarean delivery attempting TOLAC, induction of labor is not contraindicated. When induction of labor is desirable or indicated, the use of mechanical methods (Foley balloon, membrane sweeping) are recommended for cervical ripening, followed by a cautious use of oxytocin. The low-dose oxytocin protocols are preferable to high-dose regimens in women undergoing TOLAC, since low-dose oxytocin protocols are associated with a lower risk of uterine rupture.10 Cervical ripening and induction of labor using prostaglandins (misoprostol or dinoprostone) are contraindicated in the setting of TOLAC, since they geometrically increase the risk for uterine rupture.11 It is pertinent to always watch out for signs and symptoms suggestive of uterine rupture during labor in women undergoing TOLAC, including fetal intolerance during labor, loss of fetal station, sudden onset of vaginal bleeding, severe lower abdominal pain along prior cesarean delivery incision scar, and maternal hemodynamic changes (tachycardia, hypotension). It is recommended that the fetuses of women undergoing TOLAC be monitored continuously.
To effectively counsel a woman who previously has had a cesarean delivery about how she plans to deliver during a subsequent pregnancy, it is important to discuss the most frequent complications associated with TOLAC and repeat cesarean delivery. Additionally, it is important to try to include a personalized risk assessment for the likelihood of VBAC and the relative risks of maternal and perinatal morbidity. The TOLAC calculator, derived from data from the Maternal Fetal Medicine Units Network registry, is a validated tool for estimating the chance of TOLAC in the United States.12 Although not currently recommended by the American College of Obstetricians and Gynecologists (ACOG) for estimating the probability of TOLAC success, the SBS is a simple, generalizable, reproducible, and objective metric that can be used at the time of labor admission to predict the probability of VBAC. ACOG recommends offering TOLAC to carefully selected women who have had one or two prior low transverse cesarean deliveries and to counsel such women on the risks vs. benefits of TOLAC.13
- Landon MB, et al. What we have learned about trial of labor after cesarean delivery from the Maternal-Fetal Medicine Units Cesarean Registry. Semin Perinatol 2016;40:281-286.
- Landon MB, et al. Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery. N Engl J Med 2004;351:2581-2589.
- Tahseen S, et al. Vaginal birth after two caesarean sections (VBAC-2)-a systematic review with meta-analysis of success rate and adverse outcomes of VBAC-2 versus VBAC-1 and repeat (third) caesarean sections. BJOG 2010;117:5-19.
- Bujold E, et al. Modified Bishop’s score and induction of labor in patients with a previous cesarean delivery. Am J Obstet Gynecol 2004;191:1644-1648.
- Laughon SK, et al. Using a simplified Bishop score to predict vaginal delivery. Obstet Gynecol 2011;117:805-811.
- Oakes MC, et al. Simplifying the prediction of vaginal birth after cesarean delivery: Role of the cervical exam. J Matern Fetal Neonatal Med 2022; Jun 20:1-6. doi: 10.1080/14767058.2022.2086795. [Online ahead of print].
- Cheng YW, et al. Delivery after prior cesarean: Maternal morbidity and mortality. Clin Perinatol 2011;38:297-309.
- Zelop CM, et al. Effect of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor. Am J Obstet Gynecol 2000;183:1184-1186.
- Silver RM, et al. Maternal morbidity associated with multiple repeat cesarean deliveries. Obstet Gynecol 2006;107:1226-1232.
- Sentilhes L, et al. Delivery for women with a previous cesarean: Guidelines for clinical practice from the French College of Gynecologists and Obstetricians (CNGOF). Eur J Obstet Gynecol Reprod Biol 2013;170:25-32.
- Koenigbauer JT, et al. Cervical ripening after cesarean section: A prospective dual center study comparing a mechanical osmotic dilator vs. prostaglandin E2. J Perinat Med 2021;49:797-805.
- Grobman WA, et al. Prediction of vaginal birth after cesarean delivery in term gestations: A calculator without race and ethnicity. Am J Obstet Gynecol 2021;225:664.e1-664.e7.
- [No authors listed]. ACOG Practice Bulletin No. 205: Vaginal birth after cesarean delivery. Obstet Gynecol 2019;133:e110-e127.
This study demonstrated that a higher likelihood of vaginal birth after cesarean was associated with a favorable simplified Bishop score on admission. This emphasizes the need for delaying patient counseling on the choice of trial of labor after cesarean delivery until the end of pregnancy to incorporate the cervical exam into decision-making.
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