Objective: Clinical trials provide fundamental evidence used to inform healthcare decisions at patient- and population levels. It is therefore important that trials evaluate outcomes considered relevant by patients and relevant stakeholders. Although validated tools assessing other aspects of trial integrity exist, there is no tool for assessing the breadth and completeness of outcomes being measured. We have developed the Comprehensiveness of Outcome Reporting (COR) Tool to assist systematic reviewers and trialists in evaluating and choosing trial outcomes within the dynamic context of obstetrics. Methods: We identified five core outcome areas – mortality, clinical/physiological, functioning/life-impact, resource-use, and adverse events – from a published taxonomy for outcomes in medical research, and programmed an excel-based tool capable of producing a heatmap to enable users to visualize whether trial outcomes appropriately represent all outcomes areas for both mother and fetus. We used a mock-heatmap to demonstrate the tool’s utility in assessing comprehensiveness of outcome reporting in obstetric trials. Results: This excel-based tool guides users through a series of simple questions regarding the clinical trial(s) being assessed, producing a heatmap output that depicts the spread of reported outcome areas. Trends are readily interpreted with a heatmap, with over/under-reported maternal and fetal-neonatal outcome areas clearly highlighted. Conclusions: Comprehensive reporting of outcomes is necessary to ensure that interventions truly result in improved outcomes in all core areas. The COR Tool will enable systematic reviewers and trialists to determine and select outcomes with more breadth and completeness, encouraging transparency and the drawing of valid clinical conclusions. Funding: None