Intrapartum ultrasound parameters within prediction models for mode of birth in nulliparous women: a scoping review

Abstract

Intrapartum ultrasound (IPUS) provides objective measurements of foetal head descent and position. This scoping review mapped how IPUS parameters have been incorporated into prediction models for mode of birth in nulliparous women, the performance and validation reported by the included studies, and the evidence relevant to obstetric nursing and midwifery. We followed the Joanna Briggs Institute scoping review methodology and PRISMA-ScR. Ten English- and Chinese-language databases were searched until February 2026. Eligible studies developed or validated a prediction model that included at least one IPUS parameter for a mode-of-birth outcome in nulliparous women. Two reviewers independently screened the records, extracted data, and assessed the risk of bias using PROBAST. The findings were synthesised narratively and stratified according to clinical timing. Comparison with clinical-only models was outside the review scope. Nineteen cohort studies (14 prospective and 5 retrospective; 2011–2026; 64–1,020 women) were included. Sixteen studies used logistic regression, two used machine-learning approaches and one used only time-to-event modelling. The angle of progression and head–perineum distance were the most frequent sonographic predictors. Study authors reported area under the receiver operating characteristic curve values of 0.75–0.99; within-study comparisons sometimes showed higher discrimination after ultrasound parameters were added, but comparator definitions and modelling methods varied. All studies had a high risk of bias, none reported external validation and none evaluated implementation outcomes. Included studies reported potentially useful discrimination, but this review cannot establish incremental value over clinical-only models. Evidence for routine IPUS use in obstetric nursing and midwifery is insufficient. Future research should prioritise multicentre external validation, standardised measurement timing, direct comparison with clinical-only models, and co-designed implementation studies examining workflow, acceptability and woman-centred outcomes. Not applicable.