SIDS is defined as the “sudden death of an infant under one year of age which remains unexplained after a thorough case investigation….” [1]. It is a diagnosis of exclusion in that it is applied when all possible causes of death are considered, examined and ruled out. Thus, as noted in its definition, SIDS represents a death without an identifiable cause. However, researchers have consistently found that, compared to living infants, infants whose deaths are coded as SIDS are more likely to be vulnerable infants such as those born prematurely and exposed to cigarette smoke and/or to have had risk factors present at last sleep such as the presence of soft and loose bedding. Moreover, some of the anatomic, genetic and biochemical anomalies more often found in SIDS cases than in infant deaths to other causes have the capacity to render infants more susceptible to these common environmental risk factors. They do so by reducing the ability of infants to become aroused to and recover from hypoxic challenges that may result from such risks as prone sleep in soft bedding. These hypotheses underscore the biological plausibility of eliminating the sleep-related risks disproportionately found with SIDS cases and addressed by the American Academy of Pediatrics (AAP) in their guidelines on safe infant sleep.[2,3] Examples of these risk factors include failure to place infants to sleep on their backs, use of loose bedding such as pillows and quilts in the infant's sleep area, and bed sharing with a sleeping adult.

Since the advent of the national "Back to Sleep" campaign in 1994 to reduce the presence of risk factors in infant care practices, sleep environments have become safer, and the incidence of SIDS has declined by half. However, risk factors continue to be found in sleep settings. Thus, despite declines, SIDS remains the leading cause of post-neonatal infant mortality. Researchers conclude that, until causes are fully identified and treatment or preventive therapies determined, the most effective way to reduce the incidence of SIDS is to increase compliance with the safe sleep guidelines.

Sudden Unexpected Infant Death (SUID) is a grouping comprised of Sudden Infant Death Syndrome (SIDS), accidental suffocation and strangulation and ill-defined and unknown causes. SUID is used as the main analytic statistic due to diagnosis shifts in the application of its component diagnoses. SUID is now a health indicator for Healthy People 2020. All three sleep-related infant deaths share similar risk factors.

[1] Willinger M, James LS, Catz C. Defining the sudden infant death syndrome (SIDS): Deliberations of an expert panel convened by the NICHD. Pediatric Pathology 1991;11:677-684.
[2]Moon RY; Taskforce on SIDS. SIDS and other sleep-related infant deaths: Evidence base for 2016 updated recommendations for a safe infant sleeping environment. Pediatrics 2016;138:e20162940
[3]Taskforce on Sudden Infant Death Syndrome. SIDS and other sleep-related infant deaths: updated 2016 recommendations for a safe infant sleeping environment. Pediatrics 2016;138:e20162938