Results

Our search identified 5,227 individual citations. We excluded 5,096 records at the title and abstract screen, and a further 99 after screening the full paper (see Figure S2). A summary of reasons for exclusion of the full papers is presented in Table S1. Thirty-two papers relating to 26 individual core outcome sets met the inclusion criteria representing published COS related to maternal (n = 18 papers; 17 COS) and neonatal (n = 14 papers; 9 COS) health.

Study and registry characteristics

Of the 18 papers related to maternal COS, 17 were primary journal articles and one was a published conference paper (secondary paper) (outlined in Table S2). Of the 14 papers related to neonatal COS, 10 were primary journal articles three were published conference papers and one was a meeting abstract (secondary papers). Fifteen COS (58%) were published from 2017 onwards (range 2006 – 2020). All 26 COS projects were registered with COMET and 11 with CROWN: four as published and seven as ongoing projects.
Eighteen studies (69%) were published in free to view journals and three quarters were funded projects (n = 20). Of the eight COS with separately published protocols, all related COS were published from 2017 onwards. Fifteen individual systematic reviews were identified relating to 11 separate COS, with all but one COS published from 2016 onwards. Fourteen of the 26 COS (54%) were included in previous reviews. The current review includes twelve new COS (46%).

Methods used in COS development

The scope and methods for development are outlined in Table S3 and summarised in the following sections.

Scope

The scope of included studies is summarised in Table 1. While most COS were intended for research (81%), almost one in five were also recommended for clinical practice. One COS developed by ICHOM was designed specifically for clinical application.19 Of the 25 COS developed for research, most cover any intervention (81%).
[Insert Table 1 about here]

Stakeholders involvement

Stakeholder groups involvement is summarised in Table 2. Clinical experts from 18 disciplines were involved in COS development. Neonatologists (54%), obstetricians (46%) and midwives (42%) represented the largest clinical expert groups involved. Public representation was sought in 18 COS (69%). Countries represented by stakeholder groups are outlined in Table S4. Of the 18 COS for which country representation data was available, each COS stakeholder group represented a median 26 countries (range 1- 36). High income countries, as defined by the World Bank (https://www.worldbank.org/), dominated representation. Developing countries were poorly represented in almost all COS.
Patient participation and retainment was reported in 18 COS projects (Table S5). Among 18 Delphi studies, half of all stakeholders were retained at final round (Mdn = 48%, range 20 - 86%). Reported median patient participation in 13 Delphi studies was 16% (range 11 - 53%) at round one and 16% (range 2 - 61%) at the final round. It was not possible to evaluate healthcare professional participation and attrition by discipline due to limitations of joint category reporting in several studies.
[Insert Table 2 about here]

Methods used in consensus process

Methods used during the consensus process are summarised in Table 3. Commonly, the initial list of outcomes was generated by literature/systematic review (n = 19; 73%). Consensus was most often reached through electronic Delphi procedure (n = 19, 73%) using either a two- (n = 8) or three-round (n = 10) process. Around half of all COS projects used a combination of Delphi with some form of final consensus meeting (n = 15). Scoring and consensus processes were employed in 18 (69%) COS. Of these, a 9-point Likert scale was the most common procedure to score outcomes (72.2%) and the 70%/15% process (see example description in Table 3) was the most common consensus definition (67%).
[Insert Table 3 about here]

Standard of COS development

Each COS was evaluated against COS-STAD minimum standards as outlined in Table S6 and summarised in Table 4. None of the included studies met all minimum standards for COS development. Median number of standards met was 8 (range 5 – 11). For 14 COS published up to and including 2017, the medium number of standards met was 6.5 (range 5-11), while the median number of standards met for COS published from 2018 onwards was 10 (range 6 – 11).
[Insert Table 4 about here]

Scope specification (Standards 1–4)

All 26 COS (100%) described in some way the research or practice setting (Standard 1 ), health condition (Standard 2 ), population (Standard 3 ), and intervention (Standard 4 ) covered by the COS, meeting the criteria representing the scope covered by the COS. Where no specific intervention was specified, any intervention was assumed.

Stakeholders involved (Standards 5–7)

Eighteen (69%) studies met all three standards for stakeholder involvement including health professionals, researchers and patients or their representatives. Some assumptions were made regarding research and health professional stakeholder involvement. Author contribution and affiliation indicated standards were most probably met in these studies. Health care professionals and researchers were well presented in all stakeholder groups. Eighteen studies (69%) met the criteria for patient or representative involvement. While eight (31%%) did not meet this criterion, these were assumed as stakeholder involvement occurred during professional conference meetings or expert working groups.

Consensus process (Standards 8-11)

No studies met all standards for the consensus process. As such standards within this domain are addressed individually.

Standard 8: Initial list of outcomes considered both health care professionals’ and patients’ views’

Six studies (23%) met this standard, seven were unclear (27%) and 13 (50%) did not meet the standard. Those that met the standard demonstrated clear consideration of patient views by conducting either qualitative research studies of patients’ views or conducted patient interviews to generate the initial list of outcomes. Jones et al., for example, stated, ‘The list of core outcomes was developed incollaboration with the PCG consumers group….outcomes that were of importance to them’ 20 whereas Van’t Hooft et al.,21 stated ‘Patient representatives and parents were invited through social media…to share their opinions regarding outcomes relevant to preterm birth ’.