Detailed Research Plan

1. What is the problem being addressed?

A lack of high-quality, recent evidence undermines shared decision-making for women with breech pregnancies. Across the UK and internationally, women have raised concerns about a lack of support.^5,6,7,8,9,10 While some women are relieved to be offered a caesarean section (CS), other women report no other option, causing ‘stress, anger, fear and injustice,’¹¹ and in some cases long-term emotional trauma.¹² Some feel pressured to attempt an external cephalic version (ECV).^13,14,15 An ECV is a procedure to manually turn the fetus head-down using pressure on the maternal abdomen.¹⁶ Some experience the procedure as very painful, with over 10% describing it as ‘intolerable.’¹⁷ 

Some providers discourage breech births due to a lack of confidence arising from minimal experience¹⁸ and evidence that CS reduces the risk of perinatal mortality and severe morbidity compared to classical/supine methods of breech delivery (RR 0.07, 95% CI 0.02 to 0.29, one study, 1025 women).¹⁹ This is understandable but out of line with individualised decision-making.²⁰ Two year outcomes show no differences in ‘death or neurodevelopmental delay’ (RR 1.09, 95% CI 0.52 to 2.30, one study, 920 children), and more infants who had been allocated to planned CS delivery had medical problems at two years (RR 1.41, 95% CI 1.05 to 1.89, one study, 843 children).¹⁹Supporting the choice of breech birth may reduce risks in future pregnancies for both mothers and babies, such as morbidly adherent placentas and elevated levels of stillbirths.²⁰ Facilitating planned vaginal births for women who choose them also enables younger obstetricians and midwives to learn breech skills, potentially improving the safety of unexpected breech births.

Breech presentation occurs in 4% (1:25) of term pregnancies.²⁰ As many as 35-58% of women may prefer to plan a breech birth, but this is highly dependent on the type of counselling they receive.^21,22  Yet a 2014 survey of UK maternity units found that only 27% offered support for a vaginal breech birth.²³ Some hospitals have created breech clinics and/or an on-call team to revive breech skills;^24,25,26 these attract women who lack local support.^7,8In some hospitals, the vaginal breech birth rate can be as high as 6-11% of the total birth rate due to women travelling to experienced providers,^27,28 compared to 0.4% of the total birth rate in the UK.²⁹ This suggests inequity and demand for skilled breech birth care.

2. Why is this research important in terms of improving health and/or wellbeing of the public and/or to patients and health care services?

PPI work to develop this proposal confirmed research indicating women in the UK are experiencing a lack of appropriate support.^5-15 The public call for PPI participants resulted in three currently pregnant women reaching out for support, claiming they had received biased counselling with ‘no statistics,’ and their providers were unable to facilitate a vaginal breech birth. Women know they are entitled to accurate information and choice, and they know this is not good enough. 

Elective CS offers some benefits for babies but also creates risks for mothers, especially those who plan to have further children. Rising rates of morbidly adherent placenta, resulting from previous uterine scars, were highlighted in the last confidential enquiry into maternal deaths and morbidity.³⁰ High rates of CS will also have economic effects on the health service, although these are unknown in the context of breech pregnancies – a gap this work aims to address. 

The RCOG summary of evidence suggests that with skilled and experienced practitioners, breech birth may be ‘nearly as safe as cephalic birth’ (perinatal mortality per 1000: CS=0.5, cephalic birth=1, breech birth=2).²⁰ Over 96% of all term breech babies are born by CS in the UK,²⁹ and breech is the indication for 14% of all CS in countries with a low perinatal mortality rate.³¹ The majority of breech presentations occur in first pregnancies, contributing significantly to the most common indication for surgical delivery: previous CS.³¹ To reduce the CS rate for breech, most women whose babies present breech at term are recommended an ECV.¹⁶ But ECV has not been shown to improve outcomes for babies, compared to no ECV, in multiple Cochrane Reviews.³²

Up to 30% of breech presentations are also first discovered in labour,³³ when the maternal risks associated with emergency CS are higher. For example, a CS performed at full dilatation carries eight times more risk of maternal death than one performed earlier (OR 7.96 95%CI 1.61-39.39).³⁴ A loss of breech skills over the last few decades has introduced additional maternal and neonatal risks for these unexpected breech births.^10,12,35 Despite representing only 0.4% of all births,²⁹ vaginal breech births accounted for 12% of NHS litigation costs related to cerebral palsy in a recent review.³⁶ All but one of these were unexpected, with the breech presentation detected for the first time late in labour.

PBB is a proposed innovation package based on programme theory developed from previous research, summarised as follows:

• Providing reliable, experienced support for physiological breech births, in which women are encouraged to remain active and adopt the birthing position of their choice (the intervention), will improve access to and outcomes of breech births
• because this is more acceptable to women than standard care,⁵ in which skill levels are unpredictably variable and low overall (mechanism 1, Walker et al 2016a, 2017),
• and because birthing in upright positions results in shorter labours and fewer interventions, compared to the supine birthing positions prescribed in standard care (mechanism 2, Walker et al 2016b);^27,37
• but these potential benefits may only be realised in contexts where specialist multi-disciplinary teams are enabled to self-organise to support the wider maternity care team as required (context, Walker et al 2018a,c).

This package of care is partially implemented in some sites within the UK²⁵ and internationally.^4,38 But we do not know if PBB is as clinically and cost-effective as standard care in the NHS.

See TABLE 1: DESCRIPTION OF INTERVENTIONfor a comparison of PBB care with standard care.

One hospital that has implemented PBB, the Royal Jubilee Maternity Services in Belfast,²⁵ has reported an increase in term breech births (from 15% to 45% of all breech births) and primiparous breech births (from 30% to 45% of all breech births), concurrent with a reduction in neonatal admissions (from 83% to 24%).³⁹ Their results are part of a larger evaluation involving eight sites across the UK, most of which are reporting an increase in breech births following PBB training (Walker et al 2017a). If the final results are similar, PBB-based training will be the first breech educational intervention associated with improvements in both maternal and neonatal outcomes. The next step requires a more robust design – an RCT.

3. Review of existing evidence 

The Cochrane Review on ‘Planned caesarean section for term breech delivery’ reports short-term benefits for infants with no short-term differences for mothers and no long-term differences for children when planned CS is compared to planned breech birth (risk ratios outlined above).¹⁹ The review includes three trials. Each of these were conducted prior to 2000, and none of them includes physiological breech birth (PBB) methods. The review concludes by recommending research on strategies to improve the safety of vaginal breech delivery. In a secondary analysis of the largest trial, the presence of an experienced midwife or obstetrician was the only intervention demonstrated to lower risks associated with vaginal breech birth (OR: 0.30, 95% CI, 0.13-0.68, p=.004).⁴⁰

The Cochrane Review on ‘External cephalic version for breech presentation at term’ reports benefits for mothers with no significant differences for infants when ECV is compared with no ECV.³² In this review, ECV reduces the CS rate compared to no ECV (RR 0.57, 95% CI 0.40 to 0.82, evidence graded very low). None of the trials used PBB methods. The review found no significant differences in neonatal outcomes, including the incidence of Apgar score ratings below seven at one minute or five minutes, low umbilical vein pH levels, neonatal admission, and perinatal death. 

In a large UK cohort study, ECV was associated with a combined stillbirth and neonatal mortality rate of 1.9 per 1000,⁴¹ including all subsequent modes of delivery: cephalic births, breech births and CS. A population-level cohort study in the Netherlands associated planned vaginal breech birth with a perinatal mortality rate of 1.6 per 1000, and 1.3 per 1000 when cases undiagnosed before labour were excluded.⁴² Also in the Netherlands during the same period, a large series reported a perinatal mortality rate of 1.8 per 1000 following ECV.⁴³ These figures suggest near parity in neonatal outcomes between cephalic birth following ECV and breech birth. 

The cost-effectiveness of breech care options in current UK maternity care requires investigation. Clinical and cost-effectiveness of ECV is sensitive to ECV and breech birth success rates within a given setting, which vary from 14-49% in the UK.^41,44 In Denmark, Jensen and Wüst⁴⁵found that, following publication of the last Term Breech Trial,⁴⁶the increased CS rate between 2001-2004 resulted in 3.5% higher baseline costs for breech babies, equivalent to 1.5 million dollars, including follow-up to two years. A recent cost-effectiveness analysis concluded that universal ultrasound to detect term breech presentation would potentially be cost-effective in the NHS,⁴⁴but Wastlund et al’s model was based on elimination of all vaginal breech births. My PPI work and available research^5-15 indicate this is not what women want. No study has evaluated PBB care.

PBB methods (Walker et al., 2016b) include upright, active maternal birth positions. Louwen et alreported on 229 upright breech births compared to supine deliveries. Upright births were associated with significantly fewer manoeuvres (manual interventions, including forceps) (OR 0.45, 95% CI 0.31-0.68) and neonatal birth injuries (OR 0.08, 95% CI 0.01-0.58).²⁷ Second stages of labour were 42% shorter, with a non-significant decrease in serious perineal lacerations. Rates of CS in labour also decreased following the implementation of upright breech birth. In Bogner et al’s smaller study of 41 matched pairs, upright breech births were associated with a reduction in severe perineal injury from 58.5% to 14.6%, and 70% of all births took place spontaneously, without the need for manoeuvres.³⁷These improvements may impact the clinical and/or cost-effectiveness of current care recommendations for breech presentation at term and women’s experiences of care.

4. What is the research question / aims and objectives?

This research asks: Is it feasible to conduct a clinical randomised controlled trial, with economic and implementation evaluation, comparing physiological breech birth care (PBB) with standard NHS practice? (Table 1)

The aims are to:

1. Determine the feasibility of a full RCT of PBB care vs standard care for women >36 weeks pregnant;
2. Refine the PBB care programme theory through implementation process evaluation; and
3. Determine which costs and benefits to the NHS should be measured in a full RCT.

The objectives are to:

1. Identify core and secondary outcome sets for PBB research and progression criteria for a full RCT, using an on-line Delphi consensus process;
2. Identify by survey the number of UK sites willing to participate in a substantive trial;
3. Identify recruitment and retention rates to inform estimations for a full RCT; 
4. Measure the completeness of outcome data and time required to gather it;
5. Assess the acceptability and fidelity of PBB implementation;
6. Identify the relevant resources and health services used and test appropriate methods for their measurement;
7. Develop a long-term cost-effectiveness decision-model; and
8. Determine with a Trial Steering Committee (TSC) whether a trial is feasible and offers value for a future policy change.

5. Project plan

Engagement

In preparing this application, feedback was sought from service users (termbreech2020.org). This included the Fast Track Review offered by NIHR Research Design Service London of my Plain English Summary, a review of the entire application by the Birth Trauma Association and meetings with local Maternity Voices Partnership groups. Additionally, a PPI group was formed of women who had experienced a breech pregnancy in the UK within the last 5 years, with outcomes of birth after ECV, CS and vaginal breech birth represented. Invitations were circulated via social media. Five women have indicated an interest in long-term involvement with the project, along with the leaders of the groups we contacted.

Women with a strong desire for vaginal birth appear to be least satisfied with current care and have the greatest need for more evidence to underpin shared decision-making. Some women described feeling ‘very pressured by doctors’ in their pregnancies, consistent with available research. They did not necessarily want research to tell them which option is ‘best.’ Some were wary that if PBB proved ‘safe,’ women would feel just as pressured to attempt a PBB as women currently feel to accept an ECV or CS. Women prioritised individualised care. They wanted to know if it was reasonably safe to make the choice which meets their unique preferences, values and circumstances, or if one option really was significantly better than another.

PPI work influenced the decision to include 2-year health usage and quality of life outcomes at the feasibility phase. Women have been disappointed by a focus on short-term outcomes and a disregard for long-term outcomes, which research also indicates are most important to women.²¹

Women who participated in our PPI had a strong wish to contribute to a better research base for breech birth, but they also wanted reassurance no one would suffer distress due to randomisation. This influenced the decision to choose a pragmatic trial design.⁴⁸The feasibility trial compares a model of care delivery designed to support vaginal breech birth as safely as possible (PBB), with standard care, designed to minimise vaginal breech births through ECV and CS, but it does not require women to submit to one treatment or another (TABLE 1). In both arms of the trial, women can choose ECV, breech birth and/or CS. This would also happen in real world practice if PBB were rolled out more widely following a trial.

Feedback has also been sought from key hospital clinical and research staff throughout the UK. Their views also influenced the pragmatic trial design. They identified that demand for ECV, CS and breech birth is influenced by local cultural and media influences, so a restrictive, explanatory trial design could limit regional participation in a multi-centre trial and subsequent generalisability. In May, I gathered feedback from 52 professionals from participating Trusts and piloted an acceptability questionnaire. As the protocol develops, engagement events will be held with stakeholders, including service users, midwives, obstetricians, anaesthetists, neonatologists and commissioners within the South London Clinical Research Network (CRN).

PROGRAMME OF WORK

Delphi study: April – June 2020

Currently, the COMET Initiative website lists no core outcome sets for effectiveness studies related to breech birth (comet-initiative.org). Therefore, a preliminary Delphi consensus study will be conducted to develop a COMET outcome set, along with progression criteria based on them, with relevant stakeholders.⁴⁹It will involve at least 28 participants, based on my previous experience with this methodology (2016a,b, 2015a). They will be recruited via prospective sampling from local clinical leaders, national policy-making organisations (e.g. NICE, RCOG), service user representatives, and key experts in PBB practice, health economics and litigation. The process will use JISC Online Surveys software enabling anonymised responses.

In Round 1, recommendations for a core outcome set will be made based on currently available evidence, along with progression criteria related to these outcomes using the MRC/NIHR recommended traffic light system. Participants will be asked to rank them using a Likert scale (1=not important to 5=very important). Items rated as 4 or 5 by >80% of participants will be confirmed. Participants will be able to suggest changes or additional items, and items not reaching consensus will be recirculated to confirm participants’ opinions. Results will be reported and discussed at a face-to-face meeting in July 2020, to confirm the outcome set, progression criteria and clinical protocol for the small trial. I have experience facilitating such groups and ensuring all voices are heard.

Survey of UK maternity units: Jan – March 2021

The survey of UK maternity units (n=151) will collect information via an on-line survey to determine how many units are willing and able to participate in a substantive trial of PBB vs standard care (‘potential sites’). This survey will also chart the availability of vaginal breech birth services within the UK, as the only available estimates are from a conference report delivered in 2014.²³ The survey will initially be sent to Consultant Midwives or network contacts, for discussion with obstetric colleagues and response. Two follow-up phone calls will be made if no response is received.

Small feasibility trial: April – September 2021

A small feasibility trial will be conducted in four Trusts within the South London Clinical Research Network (CRN): Guy’s and St Thomas’, Kingston, Lewisham and Greenwich, and King’s. The recruitment target is a minimum of 10 women per centre and a maximum of 100 in total. The trial protocol will be completed, registered prospectively, ethically reviewed and necessary permissions obtained by 1 April 2021. The online eCRF database will be developed with MedSciNet, based on the COMET outcome set developed.

Inclusion criteria will include: Women >36 weeks pregnant with a singleton breech presentation, no absolute contraindication to vaginal birth. Exclusion criteria will include: Previous attempt at ECV in the current pregnancy. The inclusion criteria for randomisation are broad, to ensure participants in the trial are similar to the average population.⁴⁸ 

Eligible women will receive detailed information about the trial (See Table 1) at the time breech presentation is confirmed by ultrasound diagnosis after 36 weeks of pregnancy. This will include women for whom breech presentation is diagnosed for the first time in labour, as have previous breech trials.⁴⁶Consent will encompass data collection over the short and long term for mothers and their babies, until 10 years after the birth. Although this study only plans to gather data until 2 years after the birth, longer term data may emerge as important. Consent will be taken by a CRN-trained clinician not part of the research team to avoid women feeling pressured to participate. The feasibility trial will run until the recruitment target is met or September 2021.

Consenting participants will be stratified by parity (nulliparous / multiparous). Women will be randomised to either 1) standard care (control) or 2) PBB care (intervention), using the online randomisation service provided by King’s Clinical Trials Unit (KCTU).

The sample size of 100 women was calculated to enable estimation of a recruitment rate between 20-80%, with a 95% confidence interval, within ±10%. For a site with an average of 25 women it would be possible to estimate the same recruitment rate within ±18%.

A bespoke data extraction form will be devised. At the time of randomisation or consent for prospective data collection, the form will be included in the woman’s notes to record information about each relevant episode of care. The completeness of outcome data will be described, to include:

• Recruitment and retention rates
• Pooled outcomes, including: admissions to neonatal unit, vaginal birth rates, known caregiver in labour, satisfaction with care, demographic data, resource and health service use and quality of life outcomes at 3 months.

Data from the bespoke data collection forms and patient-reported questionnaires will be entered into the eCRF database by the researcher.

Implementation process evaluation 

A detailed implementation process evaluation alongside a feasibility study will increase the chances of a successful substantive trial and potentially quicken the public health impact of the intervention if it is effective.⁵⁰ The purpose of a process evaluation to inform trials of a complex interventions is to understand the effects of implementing a new intervention and the mechanisms of these effects in new contexts.^51,52 Implementation outcomes are informed by Proctor et al⁵³ and will focus on acceptability and fidelity.

Acceptabilityto staff will be assessed using questionnaires and semi-guided interviews informed by the Theoretical Acceptability Framework (TAF), designed to measure the acceptability of healthcare interventions.⁵⁴ All intrapartum care staff will be invited to complete anonymised on-line questionnaires (n=150), before and after the small feasibility trial. The questionnaires will use Likert scales to assess acceptability. Qualitative interviews will be conducted by a Research Assistant (RA) with all consenting staff who attend a planned PBB in labour (approximately 20), and with midwifery and obstetric leads (n=8).

Acceptability to women will also be evaluated using online questionnaires (n=100) informed by the TAF,⁵⁴ three months after their birth. Qualitative interviews will be conducted by the RA with a sample of women (n=5 from each site, total=20), between 3 and 4 months after birth, to include each randomisation group, mode of birth choice and a range of acceptability scores. Interviews will be held in the setting of participants’ choosing, digitally recorded and transcribed verbatim using a transcription service.

Qualitative data will be analysed iteratively, using NVivo software and grounded theory methods, as this methodology is particularly suited to understanding ‘how’ something works, or not (Walker et al 2018c). In the analysis, recurrent themes and patterns will be compared across the interviews to build an understanding of how staff view the integration of PBB into their normal practice. This will provide insight on difficulties that arise, whether they reflect a problem with the approach or its implementation and potential solutions offered by staff.⁵³ Analysis of interviews with women will help explain how women experience PBB in relation to their expectations and values.

Fidelity, the degree to which the service is delivered as planned, will be assessed using routinely collected data and case-note reviews of all participants performed by the lead researcher. These will be audited using the TIDieR checklist⁵⁵ to evaluate compliance with the trial protocol (PBB) or the Trust guideline.

The findings will be integrated to help refine the PBB programme theory and possibly make changes to the trial design, intervention or implementation process.

Two-year follow-up: April – June 2020 and 2022

Some elements of a feasibility study benefit from randomisation, and some do not require it. To assess the collection of outcome and cost data for 2-year follow-up of mothers and babies, 20 consenting women will be recruited prior to the feasibility trial. We will investigate completeness by type of data and cost for alternative methods of data collection, for example via questionnaire and search of records for health and social care service use by NHS number. This will enable identification of approaches for trial follow-up within the 3-year window of the fellowship grant.

Feasibility for economic evaluation and long-term modelling

When a full trial is conducted, PBB will only be recommended for widespread implementation if cost-effective. Health economics work at the feasibility stage is necessary to define and refine methods of data collection to enable an economic evaluation.⁵⁶Identification of implementation costs will involve seeking stakeholder views on setting up and maintaining the intervention, identifying the range of payers of costs and receivers of benefits (e.g. financial and resource savings), and different aspects of programme implementation, such as training. I am already collecting data on the time I spend liaising with stakeholders to support a deeper understanding of the costs of setting up a new service and potential trial.

Resource and health service use data will be identified for each stage of provision, to include hospital and community-based care of mother and baby prior to and during delivery and follow-up to 2 years. Economics feasibility work will focus on: design and completion of a bespoke data collection form for patient-level resource use, assessment of data collection for types of procedure, time in specific parts of the delivery suite, length of stay for mother and baby by ward, drug use and treatment of complications, use of primary care services (including home visits), use of outpatient department and any further re-admissions for mother and baby up to two years. Completion of the EQ-5D-5L⁵⁷ will be assessed as a potential outcome measure for a cost-utility analysis.  Analysis will focus on quality, quantity, cost availability and timeliness of data routinely available with that captured on the CRF and provided by mothers. Recommendations will be made for the collection and analysis of economic data alongside a future trial.

A long-term cost-effectiveness model (from 36 week scan to 2 years) will assess the likely cost-effectiveness of PBB care versus standard care, from an NHS viewpoint. Conceptual development will account for existing models, with review by the TSC. The model will be parameterised from existing literature, using the hierarchy of evidence and relevance to guide selection. It will account for the NICE reference case and good practice in decision-modelling. Challenges we expect to consider include accounting for maternal and child outcomes, and linking method of birth to both long-term morbidity as well as mortality.³⁸The model will be probabilistic and give an indication of how likely it is that PBB will be cost-effective. We will also aim to provide a value of information analysis to address the question of which uncertain parameters would provide greatest value for further research. The economic evaluation will be supported by health economist Professor Julia Fox-Rushby.

Deciding on feasibility

The final decision on whether a full RCT is feasible and offers value for a future policy change will rest with the Trial Steering Committee (TSC). It will be informed by the stoplight criteria developed with stakeholders in the Delphi consensus study and the results of all work streams. For example:

A full trial may be considered feasible on clinical grounds if:

• the annual birth rate in potential sites
• x the percentage of women expected to be recruited and retained in a trial
• x 3 (years)
• = greater than the sample needed to power a full trial to detect a difference in admissions to the neonatal unit.

A full trial may be considered feasible on acceptability grounds if:

• Among women, average acceptability scores are higher for PBB than for standard care.
• Among staff, average acceptability scores for PBB, assessed following the feasibility study, are higher than the scores for standard care, assessed prior to the feasibility study.

A full study may be considered feasible on economic grounds if modelling suggests that PBB care may potentially be cost-effective, and that a full RCT would be able to evaluate this.

6. Dissemination, Outputs and anticipated Impact

Five publications will be produced and submitted to peer-reviewed journals such as BMJ Pregnancy and Childbirth: the Delphi study, the survey of UK maternity units, the feasibility study for an RCT, the implementation process evaluation and cost-effectiveness model with discussion of wider economic issues. The publications are likely to improve the relevance and efficiency of future research concerning breech presentation and a full RCT if appropriate. Results will be shared widely at obstetric and midwifery conferences, including the annual meeting of the British Intrapartum Care Society. Information and updates about the trial will be shared on a dedicated trial website (termbreech2020.org) and on my professional blog (breechbirth.org.uk), visited daily by approximately 800 people in over 30 countries.

7. Project Management

The TSC will meet at critical points, as indicated on the timetable. Membership will include myself (CI) and one other research support team member, health economists, statisticians, two PPI representatives, an independent Chair, an observer from the NIHR and at two other independent members, a senior midwife and senior obstetrician with experience of conducting clinical trials. The TSC will fulfil the function of a Data Monitoring Committee during the feasibility study and will make an overall recommendation about the feasibility of proceeding with a full RCT, based on the study results.

8. Ethics

This research will require ethical approval from the NHS Health Research Authority (HRA) Integrated Research Application System (IRAS). 

The Research Assistant will need to be trained and skilled at conducting sensitive, emotive and potentially distressing interviews. Women may use the interviews as a way of complaining about poor care or reporting negligent care. Staff may use the interviews to disclose poor practice or concerns. The mechanisms to deal with these issues sensitively and responsibly will be clearly described in the protocol, and the participant information sheets will reflect these possibilities. For example, women who have responded to our PPI invitations with requests for help to access supportive care, I have referred to a breech-experienced midwife who is not involved in this research.

The main ethical issue will be ensuring that women have made a fully informed decision to participate in the trial, including understanding of the possible risks and benefits each care pathway may entail. Close working with the PPI group will help ensure the Participant Information Sheet for the trial is fit for this purpose.

9. Success Criteria

Success in this fellowship will be measured by completion of each segment of the work programme and submission of a publishable report by the target dates, represented by stars on the timeline. Work to obtain ethical approvals for the Delphi and maternity units surveys will begin once this application is submitted, followed by initial drafting of the feasibility trial protocol.

Minimal recruitment is always a risk. Although the pragmatic design has been chosen to reduce this, women may still be averse to randomisation. Clinical staff may also be averse to referring women due to not wanting the involvement of ‘breech team’ member in births they would normally manage independently. To mitigate this risk, potential participants will be identified by CRN midwives as well as clinicians. I have also been working closely with PIs from the participating sites to identify where barriers to recruitment might come from so solutions can be sought in advance. 

Previous research indicates successful implementation of a PBB service does not require 100% acceptance of all maternity care staff, but it does require acceptance among enough staff to ensure availability of an experienced practitioner (Walker et al 2018a). Smaller units (1000-2000 births) appear to be more successful at implementing this complex intervention,^4,25,28  possibly because establishment of a uniform approach and common philosophy is easier among a smaller number of staff. Larger units may need to rely more on practitioners willing to be on-call.²⁴To mitigate the risk of implementation failure, the pragmatic trial design gives leaders the flexibility to identify team working patterns that work in their local contexts. The implementation process evaluation will look closely at how this is accomplished, or not, to support a range of contexts.