Collaborative development of a scoping review protocol to map instruments assessing the parent–infant relationship: An International Initiative from COST Action TREASURE

Early relational health during the first 24 months of life is a key determinant of child development and wellbeing. During this postnatal period, the parent-infant relationship plays a central role in emotional regulation, bonding, and developmental trajectories. Although the broader early relational health framework encompasses the first 1,000 days of life, this scoping review focuses specifically on the postnatal phase, where parent-infant interactions are directly observable and measurable. However, existing assessment instruments vary widely in their conceptual focus, scope, and characteristics, and no comprehensive review has systematically mapped tools used to assess the parent-infant relationship during early infancy. In response to this gap, a transdisciplinary working group within the COST Action CA22114 - TREASURE collaboratively developed a scoping review protocol to systematically map instruments assessing the parent-infant relationship from birth to 24 months of age. This Brief Report describes the collaborative methodological process underpinning the protocol's development. The process followed an iterative, consensus-driven approach involving multidisciplinary experts from multiple COST member countries. Through structured online meetings, the group clarified core constructs and established the age range using the Population-Concept-Context (PCC) framework. The JBI methodology for scoping reviews was adopted and aligned with PRISMA-ScR standards to ensure transparency and reproducibility. Progressive drafting, internal peer review, and iterative refinement led to the final protocol, which was registered on the Open Science Framework (DOI: 10.17605/OSF.IO/HRVX9).The resulting protocol provides a replicable methodological framework for mapping instruments that assess the parent-infant relationship in the first two years of life. This Brief Report presents a framework for collaborative protocol development in international research networks, promoting shared knowledge generation in early relational health research and offering potential applicability to other COST initiatives.