Use of Fetal Occiput – Spinal Angle at Early Active Phase of First Stage of Labour in Predicting the Labour Outcome – A CrossSectional Observational Study

Abstract

Introduction: Fetal head deflexion plays an important role during the labour process and predicts the outcome of labour. Though traditionally it was assessed via digital examination, recent advancements in medicine have shown ultrasonographic parameters might be useful to measure of head flexion via fetal occiput-spine angle (OSA). Aim of this study was to evaluate its role. Method: We conducted a cross-sectional observational study on 292 uncomplicated singleton pregnant mothers without occiput posterior position. At early active phase of labour (OS= 4 – 6cm), angle between two tangential lines to the occipital bone and the vertebral body of the first cervical vertebra was measured as OSA. Labour progression and mode of delivery was monitored. Association between OSA and labour outcome along with the inter-observer difference was evaluated. Results: The mean OSA value was 133.88 ± 7.39°. The OSA measurement showed good inter-observer agreement (r = 0.99; p<0.001). The mean OSA was significantly less for the group of patients who had to undergo operative delivery (instrumental and cesarean) due to labour dystocia (n=37) as compared to women who had vaginal delivery (n=251), (128 ± 7.28° vs 134.83 ± 6.97°, P<0.001). The mean OSA was significantly greater for the group of patients who had a normal labour progression (n=32) as compared to women who had an abnormal progression (n=260), (134.67 ± 7.06° vs 127.47 ± 6.99°, P<0.001). Sonographic assessment of deflexion using OSA was found to be an independent predictor of labour outcome according to multivariate regression analysis. OSA value less than 127.8° was associated with abnormal labour progression and operative delivery with a good sensitivity of 86.5% & 85% respectively. However negative predictive value for operative delivery being 6.8%, suggests that multiple clinical parameters should be considered when the decision of caesarean section is made. Conclusion: Sonographic assessment of fetal head deflexion during early active phase can be used as reproducible, feasible screening parameter to predict labour progression and mode of delivery. Decision for operative delivery should be made using multiple clinical assessments.