SMART Preemie Project Summary Sudden and unexpected infant death (SUID) occurs 2-3-fold more often among preterm infants (<37 weeks’ gestation) compared to healthy, term infants (≥ 37 weeks) and 2-fold more often among non-Hispanic Black compared to non-Hispanic white infants. SUID rates have not changed in over 2 decades despite widespread public health efforts targeting the general population. We conducted a national prevalence study to ascertain adherence to American Academy of Pediatrics recommended SUID-reducing safe sleep practices (supine sleep, room sharing but not bedsharing, and nonuse of soft bedding) among preterm infants in our R01, “Study of Attitudes and Factors Effecting PREterm infant care Practices” (SAFE PREP; HD095060). Among 834 preterm infants recruited from 30 hospitals across the US, we found alarming rates of unsafe sleep practices at 4-8 weeks after hospital discharge, including 51% with non-supine sleep, 24% with bedsharing, and 59% with loose objects in the sleep space. Further, non-Hispanic Black mothers had lower rates of exclusive supine sleep compared to non-Hispanic white mothers (34% vs. 64%). We also found that attitudes about safety and vulnerability of preterm infants and messaging and modeling behaviors by health care providers were modifiable determinants of safe sleep practices among mothers of preterm infants. To address this urgent problem, in this R01 renewal application, we propose a type 1 hybrid implementation-effectiveness, cluster randomized trial, “SMART Preemie”, at 16 hospitals that participated in SAFE PREP. Leveraging our past experience, we will conduct two safe sleep interventions specifically targeting the factors we identified in SAFE PREP that influenced maternal decision-making about infant sleep practices: 1) a hospital-based intervention focused on safe sleep modeling and education; and 2) a post-discharge mobile health (“mHealth”) intervention where short, engaging videos and queries about safe sleep or shared reading (attention-matched control) will be delivered through text messaging. We will test the effectiveness of the hospital and post-discharge mHealth interventions individually and synergistically at changing maternal adherence to safe sleep practices by randomizing 16 NICUs into 4 groups (4 per group): (1) Safe Sleep hospital and Shared Reading post- discharge; (2) Shared Reading hospital and Safe Sleep post-discharge; (3) Safe Sleep hospital and Safe Sleep post-discharge; or (4) Shared Reading hospital and Shared Reading post-discharge. In Aim 1, we will test the effectiveness of the safe sleep interventions vs. control on adherence to safe sleep practices (supine sleep, room sharing without bedsharing, and avoidance of loose objects) and compare effectiveness across racial/ethnic groups. In Aim 2, we will test the extent that mediating factors identified in SAFE PREP, including attitudes and social norms, explain intervention effects on safe sleep practices. In Aim 3, using ...