Bishop Score for Assessing Cervical Readiness for Labor Induction
The Bishop score is the standard clinical tool for evaluating cervical favorability before labor induction, with a score above 8 (or >5 for the simplified version) indicating a favorable cervix and predicting higher likelihood of successful vaginal delivery. 1
Components and Scoring System
The Bishop score evaluates five cervical and fetal parameters 1, 2:
- Cervical dilation (measured in centimeters) - higher measurements indicate greater favorability 1
- Cervical effacement (expressed as percentage) - higher percentages indicate greater favorability 1
- Cervical consistency (firm vs. soft) 1
- Cervical position (posterior vs. anterior) 1
- Station of the presenting fetal part 1
Simplified Bishop Score Alternative
Research demonstrates that a simplified three-component score (dilation, station, and effacement only) performs equally well as the original five-component score 3:
- The simplified score ranges from 0-9 (versus 0-13 for the original) 3
- A simplified score >5 corresponds to the original score >8 for predicting successful induction 3
- The simplified version achieved similar positive predictive value (87.7% vs. 87.0%) and better correct classification rate (51.0% vs. 47.3%) compared to the original 3
- After cervical ripening, a favorable simplified Bishop score (>5) before oxytocin administration is associated with significantly decreased cesarean delivery rates (RR 0.35,95% CI 0.30-0.40) 4
Clinical Application for Induction Decisions
The Bishop score directly guides your choice of induction method 1, 2:
- Favorable cervix (score >8 or simplified >5): Proceed directly with oxytocin and/or artificial rupture of membranes 1, 2
- Unfavorable cervix (score ≤8 or simplified ≤5): Use cervical ripening agents first (mechanical methods like Foley catheter or prostaglandins if no prior cesarean) 1, 5
The score helps individualize timing decisions based on cervical status, with favorable scores indicating higher likelihood of successful induction 1.
Important Limitations and Caveats
The Bishop score has significant predictive limitations that you must understand 6, 7:
- The score performs poorly as a prediction tool before 40-41 weeks gestation in primiparous women 6
- One study found the Bishop score to be a "poor diagnostic test" with ROC curve analysis showing no significant difference from a non-diagnostic line 7
- The score should not be used to counsel patients regarding probability of uncomplicated vaginal delivery before labor onset at gestational ages less than 40 weeks 6
- Its primary utility is for guiding induction method selection, not necessarily predicting ultimate delivery mode 1, 2
Alternative Assessment Methods
Transvaginal ultrasound (TVUS) has been explored but offers no advantage over the Bishop score 8, 1:
- Meta-analyses show no significant difference in labor induction outcomes between TVUS and Bishop score assessment 8, 1
- The American College of Radiology states there is insufficient evidence to support routine TVUS use for predicting induction outcomes 8
- TVUS may have utility for distinguishing true from false labor (cervical length cutoff of 1.5 cm provides 81% specificity) 8, 2
Special Circumstance - Placenta Previa
For patients with placenta previa, avoid digital examination due to hemorrhage risk; use TVUS with real-time imaging instead 2.
Practical Algorithm for Clinical Use
- Perform digital cervical examination to calculate Bishop score (or simplified version) 1, 2
- If score >8 (or simplified >5): Initiate oxytocin and consider artificial rupture of membranes 1, 2
- If score ≤8 (or simplified ≤5): Begin cervical ripening with mechanical methods (preferred for safety) or prostaglandins (if no prior cesarean) 1, 5
- After cervical ripening: Reassess with Bishop score before starting oxytocin - achieving a favorable score post-ripening significantly reduces cesarean risk 4
- Avoid using the score alone to predict delivery mode before 40 weeks or to counsel patients on likelihood of vaginal delivery 6