Outcome Reporting in Clinical Trials on Kangaroo Mother Care in Newborns: A Systematic Review for the Development of Core Outcome Set.

Background: Kangaroo mother care (KMC) reduces mortality and morbidity in newborns, particularly benefiting preterm infants. However, substantial heterogeneity in the selection, measurement, and reporting of outcomes across KMC trials hinders evidence synthesis and clinical application, underscoring the urgent need for standardized core outcomes. Objective: To identify outcomes used to evaluate KMC as the foundational step toward developing a core outcome set. Methods: We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement for reporting. A comprehensive search of MEDLINE, Cochrane Library, Embase, CINAHL, CNKI, SinoMed, WanFang Data, and clinical trial registries was conducted for studies published or registered from January 1, 2014 to July 7, 2024. Risk of bias in the studies was not assessed, as the review did not focus on efficacy. Data on literature and outcomes were extracted for narrative synthesis. Outcomes were categorized using the COMET outcome taxonomy. Results: A total of 5730 studies were screened, and 292 studies were included in this review, consisting of 162 articles and 130 protocols, with a total of 112,601 participants. These studies were conducted across 40 countries, with the majority from lower-middle-income countries and upper-middle-income countries. A total of 1306 outcomes were extracted, resulting in 142 unique outcomes, which spanned 5 core areas and 29 outcome domains. The most frequently reported core area was physiological/clinical (256 studies, 87.67%), followed by the life impact (116 studies, 39.73%). In contrast, the death core area received limited attention, with only 10.96% of studies reporting mortality or survival outcomes. The most commonly reported outcome domain was general outcomes (185 studies, 63.36%), followed by pregnancy, puerperium, and perinatal outcomes (84 studies, 28.77%). The three most reported outcomes were breastfeeding outcomes (84 studies, 28.77%), weight/length/head circumference/(82 studies, 28.08%), and pain (67 studies, 22.95%). Conclusions: Current research on outcome reporting for KMC is comprehensive, covering most outcome domain across the five core areas. However, significant heterogeneity in outcome definitions and reporting exists across studies. Therefore, the development of a core outcome set for KMC is critical to reduce this heterogeneity, facilitate comparisons between studies, and enhance the integration of results into clinical practice and future research.