Bishop Score as a predictor of successful induction of labour in obese women: A retrospective cohort study in a regional tertiary centre

Abstract

Introduction Obesity is a significant concern in Australia, and worldwide. In 2011-2012, 55.7% of Australian women over the age of 18 were found to be overweight (Body Mass Index [BMI] 25-29.99) or obese (BMI >30). The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) report that approximately 50% of women who become pregnant fall into the category of overweight or obese. Maternal obesity is associated with higher rates of induction of labour (IOL), lower rates of successful IOL and higher caesarean section rates. Currently, there is little evidence exploring the influence of maternal BMI on Bishop Score and outcome of IOL. This study hypothesises that maternal obesity will lead to a lower Bishop Score at presentation, lower rates of successful IOL and higher rates of caesarean section. Aims To explore the influence of maternal obesity on Bishop Score and the outcome of IOL and delivery mode. Methods A retrospective cohort analysis of all live, term, singleton, cephalic deliveries initiated with IOL across normal BMI (18-24.99), overweight BMI (25-29.99), and obese BMI (>30) at the Townsville Hospital and Health Service (THHS), Queensland Australia, between July 2011 to June 2016. Student ttest, chi-squared test, and binary logistic regression were used for statistical analysis. Bishop Score at presentation, outcome of IOL and delivery mode were primary outcome measures. For this study a Bishop Score <5 was considered low. Results Obese women are more likely to have a low Bishop Score (<5) at presentation, compared to normal BMI women (85.82% versus 79.94%, P < 0.05), and were also more likely to require multiple methods of IOL (22.02% versus 12.09%, P < 0.05) and augmentation of labour (61.01% versus 53.24%, P < 0.05), compared to normal weight women. However, there was no difference in rate of successful IOL (0.99 [0.97-1.03], P > 0.05), vaginal delivery rate (76.25% versus 74.86% versus 71.92%, P > 0.05) or caesarean section rate (23.75% versus 25.14% versus 28.08%, P > 0.05) between weight classes. Despite a demonstrated trend of increasing caesarean section rate with increasing BMI, this study was underpowered to determine the significance of this difference. Conclusion Maternal obesity is associated with a lower Bishop Score at presentation and an increased need for multiple methods of IOL and augmentation of labour. However, maternal obesity does not decrease the likelihood of successful IOL. There was a demonstrated increased caesarean section rate in the obese population, however this study was not sufficiently powered to determine the significance of this finding.L6215699172018-04-11 <br />