Role of Transvaginal Sonographic Parameters in Predicting Outcomes of Induction of Labour: A Prospective Observational Study

Abstract

Introduction: Induction of labour is an artificial method of initiating uterine contractions before the onset of spontaneous labour, which leads to progressive cervical dilatation and effacement followed by delivery. Bishop score is the most commonly used method for assessing the favourability of the cervix. However, this method is subjective and less accurate. Transvaginal ultrasonography (TVS) has been demonstrated to be more sensitive than the Modified Bishop score in predicting successful labour induction in recent years as it avoids interobserver variations. Aim: To know the role of TVS parameters in predicting the outcome of induction of labour and to compare with the predictive power of the Modified Bishop score. Materials and Methods: This was a prospective observational study conducted between October 2019 to April 2021 in the Department of Obstetrics and Gynaecology, ESIC PGIMSR, Basaidarapur, New Delhi, India. The study was conducted on 124 pregnant women. Preinduction TVS was performed using a transvaginal probe of 6 MHz and a transabdominal probe of 3.75 MHz. Ultrasound was used to determine cervical length, posterior cervical angle, and foetal head position. Following the ultrasonographic examination, a digital examination of the cervix was done, and a score was assigned based on the Modified Bishop score. The induction of labour was performed as per hospital protocol. For the purpose of this study, the successful outcome was taken as a vaginal delivery within 24 hours from the start of induction. Data analysis was done by Statistical Package for Social Sciences (SPSS) version 25.0. McNemar’s test was used to compare sensitivity and specificity. Qualitative variables were correlated by the Chi-square test/Fisher’s exact test. Results: A total of 124 patients were selected, who underwent induction of labour. Out of these 92 (74.2%) patients who delivered vaginally, 81 patients delivered within 24 hours of induction and 11 patients delivered after 24 hours of induction, rest 32 patients delivered by Caesarean. So, the unsuccessful outcome was in 8.87% the of study population. Modified bishop score, TVS cervical length, posterior cervical angle, and foetal head position, all were found significant in predicting the successful induction of labour. Cervical length measured by ultrasonography can be used as a significant predictor of the successful induction of labour (p<0.001) with an optimum cut-off of <3.65 with sensitivity and specificity of 99.1% and 79.5% respectively. The posterior cervical angle can also be used as a significant predictor of successful induction of labour. Modified bishop score can be used as a significant predictor of successful induction of labour (p<0.001) with an optimum cut-off of >2 with sensitivity and specificity of 98.13% and 82.35% respectively. Although, all ultrasound parameters when combined and compared with the Bishop score were found to be more significant in predicting successful induction of labour. Conclusion: TVS parameters when combined were found to be more specific and sensitive as compared to the Modified Bishop score in predicting successful labour induction.