Participatory co-creation of a smartphone application using Girl-Centred-Design to support adolescent girls' health: Barriers, enablers and lessons learned across six countries.

Objectives: Adolescents have been identified as an ideal user group for digital health tools. However, currently, there is limited research exploring applied participatory methods that support adolescents in digital health intervention development across diverse real-world settings. This article introduces the Oky smartphone application, which provides menstrual health support to adolescents around the world and has a unique participatory method for local digital development - Girl-Centred-Design. This study explores three research objectives in relation to Oky's participatory method: (1) exploring how Oky's Girl-Centred-Design method supports meaningful participation with adolescents, (2) identifying Girl-Centred-Design method barriers and enablers and (3) generating Girl-Centred-Design lessons. Methods: A desk review of 224 documents was conducted, followed by 31 semi-structured qualitative interviews with personnel from six organisations implementing Oky across six countries (Burundi, Kenya, Tanzania, Nepal, Ukraine, and the Philippines). Findings were presented to implementing organisations for validation and were thematically analysed. Results: Six organisations developed smartphone applications using Oky's Girl-Centred-Design method, which supported meaningful participation in line with the World Health Organisation's definition and Hart's and Lundy's conceptual participation frameworks. Culturally grounded visuals, contents and features were co-created, and participants emerged as influential stakeholders and application ambassadors with new skills and increased confidence. Structural, contextual and cultural enablers and barriers were identified that helped or hindered Oky's Girl-Centred-Design method. Barriers were digital access gaps and cultural taboos. Enablers were peer networks, working with trusted community figures and using familiar spaces. Lessons learned were early-stage and iterative participation with girls and others to sustain participant-driven development throughout the implementation process. Intentional participant skills-building frameworks and further multi-stakeholder collaboration were outlined as future-oriented insights for optimising meaningful participation. Conclusion: Oky's Girl-Centred-Design is a meaningful participation method for co-creating digital interventions that empowers young people and responds to their needs. Practical and policy implications for future participatory approaches are outlined.