Cervical length measured by transvaginal ultrasonography versus Bishop score to predict successful labour induction in term pregnancies

OBJECTIVES To compare the value of transvaginal ultrasonographic measurement of the cervical length versus the Bishop score, prior to induction of labour, in predicting the mode of delivery within four days. MATERIALS AND METHODS This longitudinal study included 110 women (at term, singleton, vertex presentation) in whom induction of labour was performed at 37-42 weeks of gestation. Cervical length on transvaginal ultrasound and the Bishop score were assessed prior to induction according to standard protocol. Medical records were reviewed for relevant-- demographic and clinical data. Primary outcome criterion was successful vaginal delivery within 96 h. Univariate analyses and receiver operating characteristic (ROC) curves were used to examine differences between variables possibly predicting outcome. RESULTS Of the 110 women 66 were nulliparous and 44 multiparous. Vaginal delivery within 96 h was successful in 48 (73%) nulliparous and in 40 (91%) multiparous women ( i.e. in 80% of the total population). The overall rate of caesarean delivery was 17%. THERE WAS A SIGNIFICANT DIFFERENCE BETWEEN NULLIPAROUS AND MULTIPAROUS WOMEN IN AGE, CERVICAL LENGTH (MEAN IN MM IN NULLIPAROUS WOMEN: 29.31, range: 5.00-56.00; in multiparous women: 37.04, range: 12.00-56.00), Bishop score and successful induction, but no significant difference between these subgroups in neonatal outcomes. Only the Bishop score in nulliparous women showed a significant relationship between this variable and predicting successful labour induction (area under the ROC curve 0.679; standard error 0.73; p < 0.05; 95% CI: 0.536-0.823). The best cut-off value for the Bishop score was 3, with a sensitivity of 56.3% and a specificity of 72.2%. CONCLUSION In this study group significant independent prediction of vaginal delivery within 96 h is provided by the Bishop score but only in nulliparous women. Transvaginal ultrasonographic measurement of cervical length is not a significant independent predictor of vaginal delivery within 96 h.