INTRODUCTION Job satisfaction of midwives is important to prevent skill shortage. Those working in midwife-led models of care work more independently and have more responsibility. No previous study investigated if a self-initiated and self-responsible project could enhance job satisfaction of midwives working in a medical-led maternity unit. The aim of this study was therefore to assess job satisfaction before and after the implementation of such a project. METHODS This is longitudinal observational study at three time points using quantitative and qualitative methods. A total of 43 midwives working in a Swiss labor ward participated in the online surveys and in the focus group discussions. The surveys comprised questions from validated instruments to assess job satisfaction. Descriptive and multivariable time series analysis were used for quantitative and content analysis for qualitative data. RESULTS Adjusted predicted scores decreased between t 0 and t 1 , and subsequently increased at t 2 without reaching baseline values (e.g. 'professional support subscales' between t 0 and t 1 : (0.65; 95% CI: 0.45-0.86 vs 0.26; 95% CI: 0.08-0.45, p=0.005) and between t 0 and t 2 (0.65; 95% CI: 0.45-0.86 vs 0.29; 95% CI: 0.12-0.47, p=0.004). Focus group discussions revealed four themes: 'general job satisfaction', 'challenges with the implementation', 'continuity of care' and 'meaning for the mothers'. Midwives perceived the additional tasks as stressors. CONCLUSIONS The implementation of new projects might enhance work-related stress and consequently have negative impacts on job satisfaction in an early phase. Heads of institutions and policy makers should recognize the needs of support and additional resources for staff when implementing new projects.