Recruitment through social media ads and videocalls: cost, effectiveness, and lessons from the Experiences of Pregnancy study

While participant recruitment via social media is increasingly used, its cost-effectiveness remains unclear for pregnancy cohorts, especially across social media platforms and in the context of increasing threats from web robots (ie, bots) and fraudulent participants. Accordingly, we report on the implementation and results of online recruitment for a longitudinal cohort study about mental health in pregnancy and postpartum (Experiences of Pregnancy, EoP). We describe the following: (1) the cost-effectiveness of Facebook, Instagram, Reddit, and Twitter/X for recruiting individuals in their first trimester; (2) methods, experiences, and solutions for preventing bots and fraudulent participants; and (3) the representativeness of EoP compared to the US population and pregnancy cohorts recruited in person. Over 2.5 months (beginning June 2023), 574 participants were recruited at an advertising cost of US$6.19 per participant. Social media recruitment was highly time-efficient compared to in-person recruitment, reaching comparable sample sizes in 1/10th of the time. However, a range of safeguards to counter bots and fraudulent participants had to be implemented, resulting in 995 staff hours during recruitment. Experiences of Pregnancy also allowed reaching individuals without access to prenatal care but was not representative of the US population, suggesting stratified sampling would be needed to reach representativeness with online recruitment.