Sudden infant death syndrome

Darius A Loghmanee MD (Dr. Loghmanee of Advocate Children's Hospital has no relevant financial relationships to disclose.)
Matthew Balog MPH (Mr. Balog of Advocate Children’s Hospital has no relevant financial relationships to disclose.)
Usha S Appalaneni MD (

Dr. Appalaneni of Advocate Children’s Hospital has no relevant financial relationships to disclose.

Antonio Culebras MD, editor. (

Dr. Culebras of SUNY Upstate Medical University at Syracuse received an honorarium from Jazz Pharmaceuticals for a speaking engagement.

Originally released February 13, 1995; last updated August 5, 2018; expires August 5, 2021

This article includes discussion of sudden infant death syndrome, cot death, crib death, SIDS, and sudden and unexpected death in infants. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.


Sudden infant death syndrome (SIDS) is the sudden, unexpected death of an infant (<1 year old) that is unexplained by careful review of history, autopsy, and death scene investigation. The etiology of SIDS is thought to be multifactorial, and the triple risk hypothesis proposes that it is caused by the interplay between risk factors from 3 areas: 1) a specific and/or critical period of development, 2) an infant s underlying vulnerability, and 3) an environmental trigger. Accordingly, current management is directed at reducing SIDS risk through education about specific environmental exposures/situations. Environmental risk factors include prone sleeping (1994 “Back to Sleep” campaign), maternal smoking, and thermal stress (particularly head covering); reduction in the first has reduced SIDS by over one half without change in incidence of apparent life-threatening events (ALTE; previously referred to as “near miss” SIDS). In this article, the authors discuss the clinical presentation, pathophysiology, diagnostic workup, and management of SIDS.

Key points


• By definition, sudden infant death syndrome (SIDS) is of unknown cause and is a diagnosis of exclusion (unexplained after review of history, autopsy, and death scene investigation); if evidence of a specific cause of death is found, then it is not SIDS.


• SIDS affects infants less than 12 months of age, peaks between 2 to 4 months, and is less common after 6 months of age. SIDS is more common in boys and African Americans.


• The etiology of SIDS is unknown, but thought to be associated with autonomic nervous system dysregulation and impaired arousal mechanisms.


• Apparent life-threatening events (ALTE), formerly referred to as “near-miss SIDS,” have multiple causes that can include gastroesophageal reflux, seizures, acute respiratory infection, arrhythmia, or non-accidental trauma. An episode of ALTE does not increase risk of SIDS.


• Preventative measures include sleeping on the back; sleeping on a firm surface without extraneous soft bedding, clothing, toys, or positioning devices; room sharing with an adult, but not bed sharing; avoiding excessive room heat; avoiding exposure to cigarette smoke, alcohol, and drugs; frequent handwashing; and the use of pacifiers.

Historical note and terminology

Sudden infant death syndrome (SIDS) has been postulated to have existed from prehistoric times (Guntheroth 1995). The first recorded case that could be considered SIDS appears to have been an infant in the Old Testament (Bible: 1 Kings 3:19), though the infant s death was attributed to suffocation from overlying by its mother. To this day, distinguishing between accidental or intentional suffocation and SIDS in the absence of overt signs of physical violence proves difficult. In 19th-century Germany, pathologists invented an explanation that would defend mothers and nursemaids from accusations of either overlying or infanticide. Initially, they blamed enlargement of the thymus for directly suffocating the infant, failing to recognize that the thymus is typically large in infancy (Guntheroth 1993). Later pathologists theorized that sudden death was caused by status thymicolymphaticus, a fictional constitutional disorder associated with alleged hyperplasia of the thymus, but did not specify any measurements.

At the Second International Conference on Causes of Sudden Death in Infants in 1969, a definition of SIDS was proposed by Beckwith as “the sudden death of any infant or young child which is unexpected by history, and in which a thorough postmortem examination fails to demonstrate an adequate cause of death” (Beckwith 1970). This definition was further refined in 1989 by an expert panel with the National Institute of Child Health and Human Development to specify age less than 1 year old and include death scene investigation. Some have recommended exclusion of the diagnosis of SIDS if the death scene has not been visited, but that alone should not exclude the diagnosis of SIDS because it would exclude half of all probable cases (Guntheroth et al 1994). A new definition of SIDS, “the San Diego classification,” was proposed in 2004 and introduced subcategories for SIDS cases; however, it has not been universally accepted, and adjustment of the definition has been suggested (Jensen et al 2012). The necessity of a universally accepted definition is evident when considering the results of a national survey of medical examiners and coroners, in which they did not universally agree on the classification of death when given 4 different case scenarios of SIDS (Shapiro-Mendoza et al 2017).

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