Comparison of Cervical Length Measured by Transvaginal Ultrasonography and Bishop Score in Predicting Response to Labor Induction.

Background: This study aims to compare the value of the Bishop score and cervical length measurement by transvaginal ultrasonography in predicting active labor within 6 h, induction-to-delivery interval, and the duration of active labor and to estimate the most useful cutoff points for the two methods.

Methods: This is a prospective comparative study of Bishop score and cervical length measured by transvaginal sonography on 62 nulliparous subjects who underwent induction of labor.

Results: The Bishop score of the subjects ranged from two to seven (2-7). The mean Bishop in this study population was 4.37 + 1.23. The mean cervical length in this study was 25.59 + 6.07. Bishop score was highly significant ( P value < 0.0001) in predicting active phase of labor as compared to cervical length ( P  = 0.004). The best cutoff value for Bishop score to predict induction of labor within 6 h was more than 4 with sensitivity of 69% and specificity of 79%. Similarly, best cutoff value for cervical length to predict induction of labor within 6 h was less than or equal to 25 mm with sensitivity of 51% and specificity of 70%. Bishop score was more significant ( P  = 0.001) in predicting induction-to-delivery interval within 12 h as compared to cervical length ( P  = 0.01).

Conclusion: The Bishop score was superior in predicting the response to induction as compared to the cervical length measured by transvaginal ultrasonography.