S2 Checklist -

<div><p>Introduction</p><p>Suboptimal circumstances during the early life course, ranging from 100 days before conception to 1000 days following birth, significantly impact a child’s future health and well-being. To optimize these circumstances, collaboration is needed which includes professionals working in medical, social and public domains, as well as parents. This action research protocol aims to improve care for (future) parents facing suboptimal circumstances during the early life course by enhancing inter-professional, cross-domain collaboration and (future) parents-professional collaboration. By employing iterative action research cycles, we seek to foster integrated care pathways and improve continuity of care across the medical, social and public domains. The research will be conducted in Rotterdam, the Netherlands.</p><p>Methods and analysis</p><p>Four action research cycles incorporating descriptive qualitative and quantitative studies, including focus groups, questionnaires and observations with (future) parents facing suboptimal circumstances, professionals and policymakers. This intervention study will not only foster improved, integrated care around identification of the need of additional support, referral and care, but also foster the necessary conditions for a self-supporting neighbourhood care learning network of (future) parents, professionals and policymakers to encourage bidirectional feedback and enable reflection beyond a single organisation. These interventions will also be evaluated.</p><p>Dissemination</p><p>The results will be disseminated through peer-reviewed publications, layman summaries, regional and national knowledge platforms and presentations and factsheets relevant to all involved actors.</p></div>