INTRODUCTION

Induction of labour (IOL) nowadays is a common procedure in obstetric practice. The success of IOL largely depends upon "favourability" or "readiness" cervix which is traditionally assessed by manual examination and Scored as Bishop Score. However, this method is limited by subjectivity and reproducibility and though done in all the patients prior to IOL, several studies have demonstrated poor correlation between Bishop Score and outcome of labour.

OBJECTIVE

To evaluate the role of preinduction transvaginal ultrasonographic (TVS) cervical assessment in predicting labour outcome and to compare its performance against Bishop Score in patients undergoing induction of labour (IOL).

SETTING

A tertiary medical college hospital in Southern India.

DESIGN

Prospective observational and investigational study.

MATERIALS AND METHODS

Transvaginal ultrasound was performed in 131 patients who underwent labour induction at term with intact membranes and live fetus. Bishop Score was assessed by pervaginal examination and was compared with preinduction TVS cervical Score (parameters being cervical length, funneling, position of cervix and distance of presenting part from external os). Labour was induced within one hour of cervical assessment. The labour induction was considered successful if patient could get into active labour i.e., onset of regular uterine contractions (at interval of 2-3 minutes) and cervical dilatation of 4 cm or greater within 24 hours of induction.

RESULTS

Labour induction was successful in 86.9% of patients. At cut off Scores of ≥ 4, TVS cervical Score performed better than Bishop Score (Sensitivity 77% vs. 65%, Specificity 93% vs. 86%). ROC analysis indicated that Area Under Curve (AUC) was more for TVS Score (0.90, 95% CI 0.84 - 0.95), compared to Bishop Score. It was found that an increase in cervical length and distance from the os by 1 mm from their means were associated with an increase in odds for failure of induction and there by caesarean delivery by 6.5% and 11% respectively.

CONCLUSION

In women experiencing labour induction, transvaginal ultrasound score comprising of five different parameters indicated success of induction better than Bishop Score. Further, two of its components (longer cervical length and increased distance of presenting part from external os) demonstrated significant and independent prediction of the likelihood of failure of induction and risk of operative delivery.