Standard 9b: a consensus definition was described a priori
Eleven studies (42%) met the standard, providing clear evidence that consensus methods were defined a priori. In eight studies (31%) it was unclear and seven (27%) did not use consensus methods. Those that met this criterion provided clear evidence in published protocols, COMET registry entries or authors stated ‘a priori ’ consensus definition.

Standard 10: Criteria for including/dropping/adding outcomes was described a priori.

Eight studies (31%) met this standard providing clear evidence that all three elements were defined a priori through published protocols, registry entry or stated ‘a priori ’ within the body of the text specific to each element. In 18 (69%) studies it was unclear if the standard was met, commonly because all three elements were not clearly described.

Standard 11: Care was taken to avoid ambiguity of language used in the list of outcomes

Ten studies (38%) met this standard if evidence was described in either the protocol or main study paper. Perry et al. for example developed ‘lay definitions for individual outcomes’ which were reviewed by consumer group representatives,22 while the study protocol of Bogdanet et al. described ‘the questionnaire will contain lay terminology… ’.23 One study (4%) did not meet the standard, describing as a limitation, ‘illegible translated outcomes that were not included in the list ’.24 In 15 studies (58%) it was unclear if language ambiguity had been considered.

Outcomes and measurement considerations

Core outcomes, definitions, and measurement considerations described in 26 included COS are outlined in Table S7. The number of outcomes included in each COS ranged from six to 56. Maternal COS included both maternal and fetal/neonatal outcomes (Mdn = 17, range = 50), while neonatal specific COS generally included only neonatal outcomes (Mdn = 8, range = 20). To aid analysis, outcomes were organised into grouping domains (i.e. survival, maternal morbidity, neonatal morbidity, resource utilisation). Survival was common across 16 separate COS, related to maternal death, fetal and neonatal loss but only clearly defined in three COS.19,25,26 Similarly, resource utilisation was shared across 12 COS relating mainly to maternal/neonatal admission to intensive care, but definitions were only clearly defined in one COS.22
Significant overlap of outcomes between similar studies was evident. For example, eclampsia and pre-eclampsia are core outcomes outlined in six separate COS,25,27-31 but only defined in one.31 Similarly, while maternal haemorrhage is a domain shared across three separate COS, 25,32,33 a definition is only offered in one.33 Two COS (8%), related to maternity care and gastroschisis also addressed ‘how’and ‘when’ to measure outcomes.19,26 While how to measure outcomes were considered in four additional papers,33-36 clear recommendations were not reported. Although future work is planned by five COS developers to outline recommendations for how and when to measure outcomes,22-24,37,38 and is acknowledged as needed by two,30,39 17 COS offer no guidance on how or when to measure outcomes, with no reported future plans to do so.