Comparison of trans-vaginal ultrasound cervical length measurement and Bishop score in predicting successful labour induction in term pregnancies at Ahmadu Bello University Teaching Hospital Zaria

Abstract

The goal of induction of labour (IOL) is to achieve successful vaginal delivery and reduce caesarean section (CS). The gold standard method for assessing cervical status has been the use of the Bishop score (BS) which is not flawless leading to unnecessary intervention. Trans-vaginal ultrasound cervical length (CL) measurement has been compared with BS in predicting successful IOL. The objective of this study was to compare CL and BS in predicting successful IOL at Ahmadu Bello University Teaching Hospital. It was a cross sectional comparative study design conducted among pregnant women at 37-42 weeks of gestation slated for IOL between November 2017 to November 2018. Eighty-seven (87) women were recruited as participants. Each participant, had a trans-vaginal ultrasound (TVS) CL measured and each was followed by a digital cervical assessment using BS. Relevant data obtained was analysed using SPSS version 23. The significance level was considered at P< 0.05 IOL was successful in 66.2% (47) of the participants, while 15% (13) had CS. The receiver operating characteristic curve (ROC) demonstrated a better performance of the BS (AUC= 0.556, P= 0.433, CI= 0.426-0.673, PPV=52.8%) in predicting successful IOL than the TVS-CL measurement (AUC= 0.446, P=0.391, CI= 0.317-0.574) PPV=60.2%). Results further showed that the best cut off values for favourability for IOL for TVS-CL and BS were ≤2.5 cm and ≥5 respectively. The most important component of the BS predictive of successful IOL was cervical dilatation (OR= 0.603, P=0.011). TVS-CL did not demonstrate a diagnostic accuracy in predicting successful IOL in term pregnancies compared to BS.