Equitable maternity research: trial design considerations for the Obstetric Bleeding Study (OBS UK)

Background to OBS UK

The Obstetric Bleeding Study (OBS UK) is a stepped-wedge cluster randomised controlled trial implementing a post-partum haemorrhage (PPH) management bundle, using quality improvement methodology, in 36 sites across the UK. The bundle incorporates risk assessment, cumulative measurement of blood loss, stage-based multi-disciplinary escalation, and point-of-care guided resuscitation; with all four facets documented in a standardised PPH proforma. The PPH care bundle was first implemented in Wales between 2017-18 (called OBS Cymru) where it is now routine practice. Observational data reported a significant reduction in severe PPH and red blood cell transfusion (1), but the lack of randomised and concurrent control data has limited generalisability of these findings and more widespread adoption. The OBS UK trial was designed to address this knowledge gap. The primary outcome is the number of women needing a blood transfusion, with secondary clinical outcomes based on the core PPH set (2).

Importance of inclusive research

Recent reports have highlighted inequalities in maternal outcomes for patients of ethnic minority backgrounds and/or low socioeconomic status (3–5) It is therefore imperative that studies ensure those with the most to gain from improvements in care are included (e.g. the most severe cases, and high risk populations with language, educational (6), or cultural barriers (7) to participation).

Challenges of research in emergency settings and how these have been overcome in OBS UK

Prospective research where an intervention is provided on an individual basis is challenging in emergency care for a number of reasons. Recruitment requires identification of eligible candidates, informed consent, randomisation, and allocation of an intervention. Informed consent to perform an intervention and/or collect identifiable patient data needs adequate information, time and capacity to consider participation which is difficult in an emergency, especially when the patient is acutely unwell. Specific to the study of PPH, obtaining antenatal consent for all maternities would require substantial resource and might be considered unethical since only a minority of patients have a significant bleed. However, requesting consent only when a PPH is identified would potentially result in exclusion of the most severe cases (eg. due to being under general anaesthesia). In the OBS UK trial, since the care bundle is based on Royal College of Obstetricians and Gynaecologists guidance and collection of primary outcome data is non-identifiable, individual consent is not required.
 
When an intervention is a multifaceted care bundle this may require many changes in multiprofessional practice and systems. Providing standard and implementation care simultaneously is impractical and may lead to overlap in the management provided between treatment arms. Cluster randomised trials provide a potential solution by allowing for randomisation to occur at the level of the maternity unit rather than the individual, with maternity units randomly grouped into clusters.
 
In a traditional parallel cluster design, half the maternity units receive standard care and half receive the intervention throughout the study. In the OBS UK trial, a stepped-wedge cluster design allows each maternity unit to be randomised into a cluster (Sequence) where all sites receive the intervention, but the timing of switching from standard care to intervention care is the randomised parameter.  

OBS UK trial design

The stepped-wedge cluster randomised design of the OBS UK trial is illustrated in Figure 1. Each maternity unit is collecting outcome data during standard care and this will be compared to “OBS UK PPH care”.
 
Prior to randomisation, maternity units were selected based on pre-specified inclusion criteria and publicly available socioeconomic and ethnicity data to ensure that the 36 maternity units broadly represented the diversity of the UK (8).

Implementing the OBS UK care bundle

Implementing a complex maternity intervention is not without its challenges, particularly when faced with high staff turnover, significant pressure on services, and an increasingly complex patient population. There is a need for a change in practice and behaviour at a systemic level, with ‘buy-in’ required from all multi-professional maternity stakeholders. Implementation of the OBS UK care bundle is led by a local ‘champion’ team consisting of midwives, anaesthetists, obstetricians and haematologists. This team are supported over 9 months by a national implementation team that supports the local team in using quality improvement methodology to implement and evidence adoption. Due to the heterogeneity in systems across maternity units, the intervention is adapted to suit local requirements, whilst retaining core elements to allow standardisation of care. The 9-month implementation period was informed by evidence from OBS Cymru in which most of the change occurred within this time period. An integrated mixed methods process evaluation will explore the successes and challenges of implementation.

Summary

The OBS UK trial represents a unique opportunity to investigate PPH care. The cluster randomised design provides equitable access to interventions. This will allow findings that truly represent the diversity of patients utilising maternity services in the UK, including groups which may have been otherwise underrepresented when using a more traditional, individually randomised study design.

Acknowledgements

Thanks go to all OBS UK study sites for participating in the OBS UK trial.
 
This project was funded by the National Institute for Health Research (NIHR) (NIHR 152057). Point-of-care testing machines and consumables were provided free of charge by Haemonetics Corporation and Werfen. CSL Behring provided Fibrinogen concentrate free of charge for the study. These funders had no role in study design, data collection, data analysis, interpretation of data, or writing of the paper. The views expressed are those of the authors and not necessarily those of the NIHR.

References

1. Bell S, Collis R, Pallmann P, Bailey C, James K, John M, et al. Reduction in Massive Postpartum Haemorrhage and Red Blood Cell Transfusion During a National Quality Improvement Project, Obstetric Bleeding Strategy for Wales, OBS Cymru: An Observational Study. SSRN Electron J. 2020;

2. Meher S, Cuthbert A, Kirkham J, Williamson P, Abalos E, Aflaifel N, et al. Core outcome sets for prevention and treatment of postpartum haemorrhage: an international Delphi consensus study. BJOG: Int J Obstet Gynaecol. 2019;126(1):83–93.

3. Felker A, Patel R, Kotnis R, Kenyon S, Knight M. MBRRACE-UK Maternal MAIN Report 2024 V2.0 [Internet]. [cited 2025 Mar 14]. Available from: https://www.npeu.ox.ac.uk/assets/downloads/mbrrace-uk/reports/maternal-report-2024/MBRRACE-UK%20Maternal%20MAIN%20Report%202024%20V2.0%20ONLINE.pdf

4. Hindes I, Ibrahim B, Jardine J, Zenner D, Iliodromiti S. Inequalities in preterm birth in England: a national cohort study focusing on deprivation and ethnicity. Lancet. 2024;404:S78.

5. Jardine J, Walker K, Gurol-Urganci I, Webster K, Muller P, Hawdon J, et al. Adverse pregnancy outcomes attributable to socioeconomic and ethnic inequalities in England: a national cohort study. Lancet. 2021;398(10314):1905–12.

6. Taylor HA. Barriers to informed consent. Semin Oncol Nurs. 1999;15(2):89–95.

7. Halkoaho A, Pietilä AM, Ebbesen M, Karki S, Kangasniemi M. Cultural aspects related to informed consent in health research. Nurs Ethics. 2016;23(6):698–712.

8. Elsmore A, Rai T, Pallmann P, Townson J, Kotecha S, Black M, et al. The OBS UK Dashboard: an interactive tool for representative trial site selection to facilitate equality and diversity in maternity research. Trials. 2024;25(1):629.