Background <p>Annually, more than 3500 US infants die suddenly and unexpectedly. Many sudden unexpected infant deaths (SUID) are preventable with greater adherence to safe infant sleep guidelines. There are racial and socioeconomic disparities, both in adherence to these guidelines and in SUID rates. In the original Social Media and Risk-Reduction Training for Infant Care Practices (SMART) study in which 1600 mothers were randomized to receive short educational videos, focused on safe sleep vs. control, those receiving the safe sleep intervention had ~ 10% point higher rates of following safe sleep practices, with elimination of racial and socioeconomic disparities in safe sleep practices. GET SMART (Get Social Media and Risk-Reduction Training), a type 3 hybrid implementation-effectiveness cluster randomized trial, aims to determine optimal strategies to implement this safe sleep intervention in real-world conditions.</p> Methods <p>We have recruited 19 US birth hospitals in counties with high SUID rates. After a control phase, hospitals will complete, in a randomized, crossover design, both the “high touch” (HT) implementation strategy used in SMART (hospital staff introduced the program, obtained informed consent, and watched 2 videos with them) and a “low touch” (LT) strategy that uses a direct-to-consumer approach in which mothers use QR codes to sign up for the safe sleep video intervention. Implementation strategies and outcomes are grounded in the Proctor Conceptual Model of Implementation Research. We will compare the impact of the hospital-based HT and LT strategies with regards to differences in penetration (proportion of eligible mothers who sign up), equity of penetration according to income, race and ethnicity, and program cost per mother sign up. Effectiveness outcomes are adherence to 4 safe sleep practices (supine sleep position, sleep location [roomsharing without bedsharing], nonuse of soft bedding, pacifier use) after the 2-month intervention.</p> Discussion <p>Findings from this implementation-effectiveness study will inform strategies to broadly scale an easily replicated mobile-delivered video safe sleep intervention among groups with historically high rates of SUID.</p> Trial registration <p>This trial is registered on <i>ClinicalTrials.gov</i> (NCT06618586), registration date 2024-08-27.</p>