The HEALthy Brain and Child Development study (HBCD) is an ongoing prospective longitudinal study of approximately 7500 pregnant mothers and their newborn babies across 25 sites in the United States. The study digs deep into the assessments of the brain, evaluating the cognitive and emotional development of children from birth through the first 10 years of childhood. Twenty-five percent of the sample includes children who have a history of prenatal exposure to substances of abuse (alcohol, cigarettes, opiates, and marijuana). For a longitudinal study, research participant recruitment and retention are incredibly challenging, despite the enormous commitment of the researchers. This study aimed to deepen the knowledge on recruitment and retention of pregnant women in birth cohort studies and expand the insight into a more effective research engagement. The study evaluated the relationship between participant recruitment and the amount of effort needed to recruit the participants after they showed some primary interest at one enrollment site. The amount of the researchers’ engagement efforts were recorded on a weekly basis through unsolicited "cold" emails, phone calls, and texts The amount of patient recruitments were also recorded. The time interval between the first outreach from the researcher to a potential participant and the day when the participant completed the consent form was also recorded. Current data analysis suggests that researchers average 2.87 contacts (via emails, texts or calls) before a participant signs up. Also, it takes 10.25 days on average for a potential participant to enroll in the study. This one-and-a-half-week delay in enrollment aligns well with the weekly engagement efforts by the researchers, providing a reliable and consistent prediction for the overall pattern of study enrollment. Up to 75% of the participants were enrolled within 2 weeks, and a threshold of 29.125 days indicates that further contacts are no longer necessary.

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