Unsafe sleep factors are common in explained and unexplained sudden unexpected infant death (SUID) cases (younger than 1), according to a study published in Pediatrics. Researchers reported SUID rates for 2011-2017 by explained and unexplained categories using the CDC SUID Case Registry classification system. They found that 82% of the 4,929 SUID cases were categorized as unexplained. Of all cases, 73% had complete case information. Of SUIDs, 72% occurred in an unsafe sleep environment. The mortality rate for SUID was 97.3 per 100,000 live births. About 75% of the explained and possible suffocation deaths resulted from airway obstruction attributed to soft bedding. “Unsafe sleep circumstances were common among SUID cases, but data could only explain why the death occurred in approximately one in five cases (ie, those assigned to ‘explained suffocation’),” the study authors write. “Further analysis of unexplained SUID categories in the registry, augmented by continued improvements to death investigation and documentation, can generate hypotheses for physiologic or genetic research and advance our understanding of gaps in SUID investigation and groups at highest risk.”