Title : Transperineal ultrasound in labour: Bridging the gap between evidence and UK practice
Abstract:
OBJECTIVE: Transperineal ultrasound (TPU) is an emerging, evidence-based modality for intrapartum assessment, providing objective and reproducible parameters such as Angle of Progression (AoP), Head–Perineum Distance (HPD), and Midline Angle (MLA). Despite robust international evidence, its adoption in the UK remains limited, with labour management still largely reliant on subjective digital examination. This study evaluates the clinical utility of TPU in guiding instrumental vaginal delivery and improving decision-making in obstetric practice.
DESIGN: Prospective, single-centre observational study conducted in a UK obstetric unit.
METHODS: Between November 2024 and September 2025, consecutive women requiring instrumental vaginal delivery were assessed by a single experienced obstetrician. Standard abdominal ultrasound was performed to determine fetal head position, followed by TPU before intervention. The primary parameter assessed was the Angle of Progression (AoP), defined as the angle between the long axis of the pubic symphysis and a line drawn from its inferior border tangential to the leading edge of the fetal skull. AoP measurements were recorded and correlated with delivery outcomes.
RESULTS: Twenty-five instrumental deliveries were included. Abdominal ultrasound demonstrated Occiput Posterior/Transverse (OP) position in 24 cases and Occiput Anterior (OA) in one case. Successful vaginal delivery was achieved in 23/25 cases (92%), predominantly using rotational vacuum (Kiwi cup). In all successful cases, AoP was ≥120°, demonstrating strong predictive value. The two failed instrumental deliveries (one OA, one OP) were associated with less favourable TPU findings (AoP <120°). Maternal morbidity was low: one second-degree tear, one 3a tear following sequential instrumentation, one 3b tear, and one postpartum haemorrhage >2L. No significant neonatal morbidity was observed. Although HPD and MLA were assessed, these measurements were not consistently obtainable due to technical limitations in labour, including oedematous perineal tissues. Therefore, analysis focused on AoP, which was reliably measured in all cases.
CONCLUSION: This study provides contemporary UK data supporting TPU as a clinically valuable adjunct in labour. AoP ≥120° demonstrated strong predictive accuracy for successful instrumental delivery, consistent with international evidence, and offers an objective alternative to subjective clinical assessment. TPU has the potential to reduce failed instrumental deliveries, optimise instrument selection, and improve maternal outcomes. Despite this, uptake in the UK remains limited, highlighting a gap between evidence and practice. Wider implementation, structured training, and multicentre studies are needed. TPU represents a step towards precision obstetrics and improved intrapartum decision-making. The relatively small sample size reflects the early adoption phase and single-operator design of the study.
