A developmental evaluation was undertaken to evaluate a prototype test of a new model of perinatal healthcare across acute maternity, public health, and primary care in two hospitals in a large health authority. The project was initiated to bridge gaps in care across the acute and community settings to ensure a seamless perinatal healthcare journey for women. The objective of the evaluation was to support the prototyping process by providing data to inform decisions as the prototype was developed and by documenting decisions as they were made. This article explores challenges faced during the evaluation, including unfamiliarity of the health sector with prototype projects and their inherent uncertainty, a disconnect between the rapid pace of a prototype project and bureaucratic hurdles of working within a large organization, and high leadership turnover throughout the project. How these challenges were addressed, and the lessons learned for future evaluations, are discussed.