Introduction
Mental health interventions have traditionally been developed by clinicians and researchers without the meaningful engagement and partnership with those who would receive, deliver, and fund them. Recent progress has highlighted the importance of the co-design of interventions, through stakeholder participation, as a means of increasing the integration of mental health interventions into existing health, education, and social care systems. This protocol describes the pre-implementation phase of the INSPIRE (Innovative approaches to adolescent perinatal wellbeing) project which aims to identify challenges, and design and test interventions to promote mental wellbeing and good mental health of adolescent girls during pregnancy and the year after birth with local stakeholders in Kenya and Mozambique.

Methods
A participatory approach that blends human-centred design, systems thinking, and implementation science methods will be used to engage adolescents (aged 15–19 years), their families, and other stakeholders who can influence implementation efforts, in planning and preparing interventions. First, an understanding of context, barriers, and opportunities related to adolescent perinatal mental health will be elicited through individual interviews, focus group discussions, and observations. This will be complemented by a scoping review of relevant interventions. The research team will identify contextual insights relating to adolescent and system characteristics, strengths, and challenges. These will be shared with and refined by stakeholders. Thematic analysis will be conducted to describe the experiences of adolescent girls, and barriers and enablers to maintaining good mental health. The former will be triangulated with the Context and Implementation of Complex Intervention (CICI) framework. Causal loop diagrams will be developed to illustrate the individual and system-level variables which influence adolescent perinatal mental health.

Stakeholder workshops will be used to identify priorities, brainstorm potential interventions, develop a program theory, and prototype an intervention and implementation strategies. Intervention acceptability, appropriateness, and feasibility will be assessed, and a theory of change map finalized.

Results
To date the study has recruited 169 participants to complete individual interviews, focus group discussions and observation activities.

Conclusions
It is anticipated that the use of a participatory and systematic approach to the development of an intervention to improve mental health, will improve its perceived appropriateness, acceptability, and feasibility among key stakeholders. This may, in turn, significantly improve its availability, uptake, and sustainability.