How do you recruit and retain a prebirth cohort? Lessons learnt from growing up in New Zealand.

Growing Up in New Zealand, a longitudinal study following nearly 7,000 children, has faced some unique challenges in identifying, enrolling, and retaining a large and diverse antenatal cohort. Identification of a study region with population demographics that enabled enrollment of an appropriately diverse sample was required as was intensive community and participant engagement in order to promote the study. Complementary methods used included direct engagement with prospective participants and the community and indirect engagement via media. Thus far, retention rates above 95% have been achieved by maintaining a multimethod approach that includes valuing participants and building trusting relationships, strong brand recognition, community engagement, maintenance of participant contact and location records, ensuring high-quality interactions between the participants and the study, pretesting measures and methods prior to the main cohort, and using participant feedback to inform the measures and methods used in future waves of data collection.