319: Simplifying the bishop score

Abstract

The original Bishop score was created in the 1960's without modern statistical methods. As the five components are correlated, it is unclear whether all components are useful in predicting vaginal delivery. Our objective was to determine whether a simplified Bishop score can predict vaginal delivery equally well in contemporary obstetrical practice. Retrospectively collected data from electronic medical records of 12 clinical centers across the United States containing 228,668 deliveries from 2002 to 2008 from the Consortium on Safe Labor were used. We included women with a singleton, delivering between 37 0/7 – 41 6/7 weeks of gestation, nulliparous, vertex undergoing induction that was elective, postdates, for rupture of membranes, or induction for precursors that could have been expectantly managed, and had all five sub-components of the Bishop score recorded. Excluded were previous uterine scar, stillbirth and congenital anomalies. Logistic regression was performed, interactions explored, correlation coefficients calculated, and receiver operating characteristic (ROC) curves created with positive and negative predictive values (PPV and NPV) and likelihood ratio tests (LR). There were 6900 women who met inclusion criteria and 84.0% had a vaginal delivery. In the regression model, only dilation, effacement and station were significantly associated with vaginal delivery (p < .001). There were no significant interactions between these subscores, although they were correlated (Spearman r = .3 to .5, p < .001). The area under the ROC curve = .81 for the original Bishop score compared to .82 using a simplified score with dilation, effacement and station. The PPV, NPV and LR positive were also similar for the original Bishop score compared to using a simplified Bishop score (Table).TablePredictive characteristics of Bishop score versus simplified Bishop score.ScorePositive predictive value %Negative predictive value %Likelihood ratio positiveBishop > 891.821.22.15Simplified Bishop (Dilation, Effacement, Station only) > 592.223.22.27 Open table in a new tab In this uncomplicated nulliparous population of women at term, the Bishop score can be simplified to three components: dilation, effacement and station.