Background: Perinatal depression (depression during pregnancy or the first year postpartum) affects 10%-25% of perinatal individuals, with a higher risk among youths aged <25 years. The Mothers and Babies Course (MB) is an evidence-based intervention for the prevention of perinatal depression, grounded in cognitive behavioral therapy, attachment theory, and psychoeducation., Objective: We developed a digital adaptation of MB (Interactive Maternal Group for Information and Emotional Support [IMAGINE]) and evaluated it in a pre-post mixed methods pilot among young perinatal people in the United States., Methods: IMAGINE was a structured digital group of up to 7 participants, with scheduled MB content and open discussion for 12 weeks, facilitated by a social worker. Scheduled content included asynchronous SMS text messages, graphics, prerecorded videos, mood polls, and optional weekly synchronous video calls. Eligible participants were pregnant or ≤80 days postpartum, aged 16 to 24 years, had access to a smartphone, spoke English, and had a Patient Health Questionnaire score <10. Participants were recruited throughout the United States from August 2020 to January 2021 through paid social media ads, in-person outreach at clinics, and respondent-driven sampling. Participants completed quantitative questionnaires at enrollment and 3 months, and qualitative interviews at 3 months. We determined uptake, acceptability (by Acceptability of Intervention Measure score), and utility (by use of cognitive behavioral therapy skills). We compared depression symptoms (by Patient Health Questionnaire score), social support (by abbreviated Social Support Behavior score), and perceived stress (by Perceived Stress Score) between enrollment and follow-up by paired 2-tailed t test., Results: Among 68 individuals who contacted this study, 22 were screened, 13 were eligible, and 10 enrolled, for an uptake of 76.9%. Furthermore, 4 (40%) participants were pregnant at enrollment. Participants had a median age of 17.9 (IQR 17.4-21.7) years, 6 (67%) identified as Black, 5 (56%) Latinx, and 6 (67%) using Medicaid health insurance. Further, 9 (90%) participants completed follow-up. Among these, the mean acceptability score was 4.3 out of 5 (SD 0.6) and all participants said they would recommend IMAGINE to a friend. Participants reported using a median of 7 of 11 skills (IQR 5-7 skills) at least half the days. We found no significant changes in depression symptoms, perceived stress, or social support. Qualitatively, participants reported one-to-one support from the facilitator, connection with other parents, and regular mood reflection were especially helpful aspects of the intervention. Additionally, participants reported that the intervention normalized their mental health challenges, improved their ability to manage their mood, and increased their openness to mental health care., Conclusions: This pilot study provides promising evidence of the acceptability and utility of IMAGINE among perinatal youths. Our study's small sample size did not detect changes in clinical outcomes; our findings suggest IMAGINE warrants larger-scale evaluation., (©Keshet Ronen, Anupa Gewali, Kristin Dachelet, Erica White, Marimirca Jean-Baptiste, Yolanda N Evans, Jennifer A Unger, S Darius Tandon, Amritha Bhat. Originally published in JMIR Formative Research (https://formative.jmir.org), 02.02.2024.)