Assessing the difficulty of forceps delivery using a transperineal ultrasonographic station: a prospective cohort study.

Purpose: To investigate the clinical utility of a novel transperineal ultrasonographic (TUS) parameter, the TUS station, for assessing labour progression and predicting forceps delivery difficulty.

Methods: In this prospective cohort study, 384 TUS images from 144 participants who delivered vaginally between January 2019 and December 2021 were assessed for labour progression in a single tertiary perinatal center in Japan. Singleton cephalic pregnancies ≥ 37 weeks were included. The digital vaginal examination (DVE) findings, TUS station, and angle of progression (AoP), an ultrasound parameter commonly used for assessing labour progression, were obtained by individual obstetricians who were blinded to the results in all cases. The TUS station and DVE findings and AoP and DVE findings of the participants were compared. A second cohort requiring forceps delivery was analyzed to explore the relationship between TUS station and delivery difficulty.

Results: In the quantitative assessment of fetal head descent, the TUS station correlated with DVE findings. During the resting phase of labour, the TUS cut-off value for an easy forceps delivery was 2 cm, with a sensitivity of 85%; the maximum AUC value was 0.9 (95% confidence interval [CI]: 0.73-0.96). At the time of labour, the TUS cut-off value for an easy forceps delivery was 2.9 cm, with a sensitivity of 85%; the maximum AUC value was 0.8 (95% CI 0.65-0.96).

Conclusion: The TUS station may serve as a valuable and objective parameter for consideration in decisions regarding forceps delivery.