The distribution and predictive value of Bishop scores in nulliparas between 37 and 42 weeks gestation

Objective. The natural distribution and predictive accuracy of Bishop scores was evaluated to predict cesarean delivery (CD) in nulliparas between 37 and 42 weeks gestation. Study design. Subjects underwent serial digital cervical examinations. The Bishop score was evaluated as a binary and continuous factor to predict CD at each gestational week beginning at 37 weeks. Bishop scores were categorized as <= 5 or > 5, and CD rates were compared across Bishop score categories using chi-square or Fisher exact tests at each gestational week beginning at 37 weeks. Results. In all, 171 patients were prospectively followed. The overall CD rate was 27.5%. The prevalence of unfavorable Bishop scores, categorized as <= 5, decreased with increasing gestation age until 41 weeks. CD rates for the cohort with unfavorable Bishop scores was higher than those with favorable scores at each week. The likelihood ratio for CD was 1.35-2.00, depending on gestational age. The Bishop score that best predicted subsequent vaginal delivery following expectant management was > 3 at 37 weeks and > 5 at 39 weeks. Conclusion. A Bishop score <= 5 between 37 and 39 weeks gestation predicts a higher CD rate compared to patients with a Bishop score > 5 implying an intrinsically higher CD risk despite expectant management.