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VP57.01: Measurement of the angle of progression before labour onset in routine obstetric triage setting: can it assist in predicting the mode of delivery?

Objectives: The angle of progression (AOP) has been proposed to be a useful anteand intrapartum tool in the prediction of the mode of delivery and an AOP of 92◦ –95◦ before onset of labour was associated with a high rate of vaginal birth. Our aim was to assess whether measurement of the AOP before the onset of labour in routine labour and delivery triage setting can predict a successful vaginal delivery (VD). Methods: This was a retrospective cohort study including nulliparous women with singleton term pregnancies that presented to our labour and delivery room before onset of labour between Feb. 2017 and Jan. 2020 and underwent a routine transperineal ultrasound assessment with AOP measurement. Women were included in the study if the last AOP measurement was performed within one week of delivery. The predictive value of an AOP cut-off of 95◦ was assessed. Results: Of the 585 women included in this study, 497 (85%) had a vaginal delivery and 88 (15%) a Caesarean delivery (CD). The mean AOP was wider in women that delivered vaginally than in those who had a CD (94◦ ± 11 vs. 86◦ ± 10, p < 0.001). Women with a prelabour AOP ≥95◦ had a significantly higher rate of VD compared to those with a narrower AOP (93% vs. 79%, p < 0.001). When including only CD due to protracted labour in the analysis, only 4% of women with a prelabour AOP≥95◦ underwent CD. Multivariate stepwise logistic regression analysis demonstrated that the AOP and spontaneous onset of labour independently predicted VD. Similarly, subgroup analysis of women who underwent labour induction demonstrated a 92% VD rate in those with an AOP≥95◦. Conclusions: In routine clinical practice, measurement of the AOP before labour onset can assist in the prediction of vaginal delivery even when performed by non-experienced sonographers.