A Core Outcome Set to Guide Future Research on Caesarean Scar Ectopic Pregnancy: COSCAR Consensus Study

Objective: To develop a core outcome set (COS) for research on caesarean scar ectopic pregnancy (CSEP) treatment. Design: Consensus development study. Setting: International. Population: Healthcare professionals, researchers, patient advocates, or individuals with lived experience of CSEP. Methods: The Delphi process was conducted from July to November 2024 following a systematic review and interviews with individuals with lived experience of CSEP, which identified potential outcomes. This process followed COMET guidance. Outcomes were presented in a two-round online Delphi survey. Round one included 287 healthcare professionals, 50 researchers, and 69 patient advocates and individuals with lived experience from 51 countries. In round two, 281 participants from 43 countries contributed. The final COS was developed at a consensus meeting of the steering committee, comprising all key stakeholders. Results: 346 outcomes were initially identified, reduced to 62 in round one, then 40 in round two of the Delphi survey. The final COS comprises 19 core outcomes across seven domains: (1) Treatment success in early CSEP; (2) Complications in early treated CSEP; (3) Success of expectantly managed advanced live CSEP; (4) Complications of expectantly managed advanced live CSEP; (5) Mortality and severe morbidity; (6) Future reproductive health; and (7) Patient experience. Additionally, 15 non-mandatory outcomes and four essential reporting items were recommended. Clear definitions were provided for each core outcome. Conclusion: Through international consensus, we have developed a COS that reflects the perspectives of healthcare professionals, researchers, and individuals with lived experience of CSEP. This COS allows for standardised outcome reporting in future research, fostering a new generation of high-quality evidence that can inform clinical guidelines and ultimately improve patient outcomes.