Abstract Background Health risk behaviors during pregnancy are major risk factors for adverse health outcomes for mother and child, and they are more prevalent among vulnerable pregnant women. However, interventions often do not sufficiently meet the needs of disadvantaged groups. Changing behavior is more likely when people feel autonomous and when a behavior aligns with our identity (how we see ourselves). Despite the clear importance of identity in health behavior change, very few identity- based interventions exist for pregnant women, let alone for vulnerable pregnant women. Through co-creation, this study aims to develop an identity- and autonomy- based training program and conversation tool tailored to the needs and preferences of healthcare professionals and vulnerable pregnant women. Methods Four co-creation sessions were conducted with five professionals from medical and social domains, and five (expectant) parents in vulnerable situations. The Participatory Learning and Action research methodology was applied to ensure an equal and democratic process in designing the training and conversation tool. Results The training for professionals will focus on enhancing knowledge about the importance of identity and autonomy in behavior change, and on improving their self-efficacy through practicing the conversation tool. Example of the conversation tool, which can be integrated into daily practice, is a comic strip illustrating the conflict of being a smoker and a mother. Conclusions During intervention development, it is important to consider the needs and preferences of end-users, particularly for whom few appropriate interventions exist. Involving end-users yields valuable insights for feasible (e.g. one-consultation time frame) and accessible (e.g. easy-to-understand language) interventions. This study aligns with public health efforts toward early intervention and health promotion among vulnerable groups. Key messages • During intervention development, it is important to consider the needs and preferences of end-users. • This study aligns with public health efforts toward early intervention and health promotion among vulnerable groups.