Use of intrapartum ultrasound before assisted vaginal delivery in a single hospital in ‎Hong Kong

Objectives: To investigate the use of intrapartum ultrasound (ITU) under different indications for assisted vaginal delivery, as well as the frequencies of assessment of various ITU parameters, by clinicians in a single hospital. Methods: Medical records of women who underwent assisted vaginal delivery at Kwong Wah Hospital between 3 January 2023 and 2 January 2024 were retrospectively reviewed. Seven ITU parameters were recorded: spine position, head position, angle of progression (AoP), head-perineum distance (HPD), head direction, asynclitism, and size of caput succedaneum. Results: In total, 113 assisted vaginal deliveries were included in the analysis, comprising ventouse extraction (n=94), forceps delivery (n=17), and sequential instrumental birth (n=2). There were no failed assisted vaginal deliveries. Of the 113 assisted vaginal deliveries, 70 (61.9%) had prior ITU for indications of prolonged second stage (n=46), fetal distress (n=20), and maternal medical conditions (n=4); the respective ITU use rates were 92.0%, 35.7%, and 57.1% (p<0.001]). Among the 70 assisted vaginal deliveries with prior ITU, 29 (41.4%) had all seven sonographic parameters assessed before making the decision for assisted vaginal delivery. HPD and AoP were assessed in all cases, followed by spine position (92.9%), size of caput succedaneum (80.0%), asynclitism (78.6%), head position (62.9%), and head direction (42.9%). The frequencies of assessment among parameters differed significantly (p<0.001). Asynclitism and size of caput succedaneum were assessed least frequently than head and spine position, as well as station and descent (as measured by HPD, AoP, or head direction). Conclusion: The rate of using ITU to assess labour progress prior to assisted vaginal delivery for prolonged second stage was high at our hospital under the opt-out protocol. Sonographic assessment of fetal spine position and head station (via HPD and AoP) were most commonly assessed. The opt-out protocol may encourage ITU use, particularly in cases of delayed second stage, while preserving clinicians’ independent judgement.