Modified Bishop Score
The modified Bishop score is a cervical assessment tool that adds 2 points to the original Bishop score for multiparous women with a prior vaginal delivery, and a score of less than 5 indicates an unfavorable cervix requiring cervical ripening before labor induction. 1
Definition and Calculation
The modified Bishop score builds upon the original Bishop scoring system by incorporating parity as a predictive factor for successful labor induction 2:
- For nulliparous women: The modified Bishop score equals the standard Bishop score (0 points added)
- For multiparous women with prior vaginal delivery: Add 2 points to the standard Bishop score 2
The standard Bishop score components assess five cervical and fetal parameters (dilation, effacement, station, consistency, and position), with scores ranging from 0-13 3.
Clinical Significance for Cervical Favorability
An unfavorable cervix is defined as a modified Bishop score <5, which necessitates the use of cervical ripening agents before proceeding with labor induction. 1
This threshold is clinically important because:
- In the landmark ARRIVE trial, 63% of enrolled women had an unfavorable cervix (modified Bishop score <5) at randomization, and cervical ripening was specifically requested for these patients 1
- The modified Bishop score ≥6 is independently associated with successful vaginal birth after cesarean (VBAC), with an odds ratio of 2.07 (95% CI 1.28-3.35) 4
Predictive Value for Successful Induction
The modified Bishop score demonstrates superior predictive accuracy compared to the standard Bishop score, particularly when parity is incorporated 2, 5:
- Scores including parity (such as the simplified Bishop including parity, Hughey, and Levine scores) achieve the highest area under the curve (AUC 0.68-0.70) for predicting successful labor induction, even in women with very unfavorable cervices 5
- For labor induction with intravenous oxytocin, a modified Bishop score of 6 serves as a practical cutoff for predicting success 6
- The cesarean delivery rate for failed induction is significantly higher in nulliparous women compared to multiparous women at equivalent modified Bishop scores of 7-9 2
Clinical Application Caveats
Parity is a critical independent predictor of induction success that must be factored into clinical decision-making. 2, 5 The addition of 2 points for multiparity does not artificially inflate success rates or increase cesarean risk when the modified Bishop score ranges from 7-9 2.
When comparing assessment methods, transvaginal sonography for cervical length measurement (cutoff 2.5 cm) demonstrates higher sensitivity (61.8%) than modified Bishop score (28.9%) for predicting successful induction, though both methods maintain excellent specificity 6.