How to Efficiently Recruit Participants in a Perinatal Cohort Study: CAN-B Cohort Strategies/Lessons Learned

In the context of the Cannabis Antenatal and Neurodevelopment of Babies (CAN-B) cohort study, we describe our experience identifying the most effective recruitment strategy to meet enrolment objectives by comparing interest, enrolment rates, and cost-efficiency across multiple approaches.

From May 2022 to August 2025, at the obstetrical ultrasound unit of Sherbrooke University Hospital Center (CHUS), 4 recruitment strategies were successively implemented: (1) a study flyer given by care providers (May-September 2022), (2) recruitment by phone (October-November 2022); (3) a study flyer given by care providers or part time in-person study presentation by research team (December 2022-May 2023), and (4) full time in-person presentation of the study by the research team (June 2023-August 2025). Interest, enrolment rate and cost-effectiveness were compared.

At CHUS, which has approximately 3000 annual births, 185 participants were enrolled, including 115 pregnant cannabis users. The proportion of cannabis users among women approached ranged from 7% to 17%. The fourth strategy yielded the highest enrolment rate (3 cannabis users/month) with high interest (71%), compared with strategies 1 (2/month;100% interest), 2 (1/month; 64% interest), and 3 (2/month; 55% interest). Recruitment by phone was the costliest despite suboptimal performance. Although the first strategy was the least costly, the fourth was retained due to superior recruitment outcomes.

Our experience demonstrates that pregnant women, including cannabis users, are interested in clinical research. Implementing an active recruitment strategy that enables direct interaction between research staff and pregnant women can increase both interest and enrolment rates.