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Key Features

  • Sudden, unexplained death of an infant or child

  • Sudden unexpected infant death (SUID) is gaining favor as preferred term to refer infant deaths that were classified as sudden infant death syndrome (SIDS)

  • SUID

    • Defined as any sudden and unexpected infant death, whether explained (such as accidental suffocation or strangulation) or unexplained (such as SIDS)

    • Includes deaths due to infection, ingestions, metabolic diseases, cardiac arrhythmias, and trauma

    • New evidence shows that the incidence of accidental suffocation and strangulation in bed is increasing due to unsafe sleep surfaces and environments

  • SIDS

    • Neither a true diagnosis nor a syndrome

    • Defined as the sudden death of an infant younger than 1 year that remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history

    • Postmortem examination is an important feature of the definition because approximately 20% of cases of sudden death can be explained by autopsy findings


  • Deaths peak between ages 2 and 4 months

  • Most deaths occur between midnight and 8:00 AM

  • SUID is more common among ethnic and racial minorities and socioeconomically disadvantaged populations

  • Racial disparity in the prevalence of prone positioning and especially in bed-sharing may be contributing to the continued disparity in SUID rates between black and white infants

  • There is a 3:2 male predominance in most series

  • Other risk factors

    • Premature birth

    • Low birth weight

    • Recent infection

    • Young maternal age

    • Maternal tobacco or drug use

    • High maternal parity

    • Crowded living conditions

Clinical Findings

  • The most consistent pathologic findings in SUID deaths from unknown cause (previously classified as SIDS) are intrathoracic petechiae and mild inflammation and congestion of the respiratory tract

  • More subtle pathologic findings include

    • Brainstem gliosis

    • Extramedullary hematopoiesis

    • Increases in peri-adrenal brown fat

  • When a distinct cause cannot be identified, the mechanism or mechanisms of death in SUID are unknown; hypotheses include

    • upper airway obstruction

    • catecholamine excess

    • increased fetal hemoglobin

    • Maldevelopment or delayed maturation of the brainstem, which is responsible for arousal from sleep, remains the predominant theory

  • A history of mild symptoms of upper respiratory infection before death is not uncommon


  • Modifiable risk factors include

    • Sleep position, location, and environment

    • Formula feeding

    • Maternal smoking or drug use

    • Infant overheating

  • The prone sleep position may increase the risk of SUID through decreased arousal or rebreathing of exhaled gases

  • Side positioning, often used in hospitals and then mimicked at home, increases risk of SUID compared with the supine position and is not a safe alternative to supine sleep, even in infants with reflux

  • Environmental smoke exposure, especially prenatal maternal smoking, increases the risk of SUID

  • Risk of SUID is lower when an infant is breastfed and when a pacifier is offered at naptime and bedtime

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