Direct engagement boosts recruitment of pregnant cannabis users in research

The Cannabis Antenatal and Neurodevelopment of Babies (CAN-B) cohort study evaluated the most effective strategies to recruit pregnant women, including cannabis users, into a longitudinal research program. Over three years at a major Canadian hospital with approximately 3,000 annual births, researchers tested four recruitment approaches: study flyers distributed by healthcare providers, phone-based recruitment, hybrid flyer and in-person presentations, and full-time in-person recruitment by research staff. The study successfully enrolled 185 participants, including 115 pregnant cannabis users, demonstrating that this population is willing to participate in clinical research examining potential health impacts.

The research reveals that direct, in-person engagement by research staff proved most effective, achieving the highest enrollment rate of 3 cannabis users per month with 71% interest among approached women. In contrast, phone-based recruitment was the most expensive strategy but yielded the poorest results (only 1 user per month). While the initial low-cost flyer distribution strategy generated strong initial interest (100%), it ultimately recruited fewer participants than the resource-intensive but highly interactive approach. The findings highlight an important paradox in research recruitment: the most cost-effective method isn't always the most effective for meeting enrollment targets.

These results have significant implications for future studies examining perinatal cannabis use and fetal neurodevelopment. By demonstrating that pregnant women—including those using cannabis—actively seek opportunities to contribute to medical research, the study encourages researchers to invest in direct recruitment strategies despite higher upfront costs. The CAN-B cohort's experience suggests that visible, relatable research staff presence builds trust and increases participation rates, which is particularly important for studying sensitive topics like substance use in pregnancy where stigma and privacy concerns might otherwise discourage enrollment.