Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) describes the sudden death of an otherwise healthy infant (< 1 year of age) with no identifiable cause. Sudden infant death syndrome is the leading cause of death in children between 1 and 12 months of age in the United States. Sudden infant death syndrome is a diagnosis of exclusion and can only be confirmed after other causes of death have been ruled out with a thorough medical history and autopsy. Providing parents with preventative education is key to reducing the risk of SIDS. Preventative measures include having infants sleep supine, on firm surfaces, with no clutter in their crib.

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Definition and Epidemiology


Sudden infant death syndrome (SIDS) is the sudden, unexplained death of a child in infancy (< 1 year of age) with no identifiable cause after examination, clinical case review, and autopsy.


  • Leading cause of death in children between 1 and 12 months of age in the United States
    • Peak incidence: 2–4 months
    • > 90% occur before 6 months of age
  • Annual incidence: 0.5 per 1,000 live births
  • Nearly 3 times as common in Black and Native American/Alaskan Native families
  • The incidence of SIDS has significantly decreased in developing countries due to “back to sleep” public health campaigns.
SUID 1990-2018

Mortality due to sudden infant death syndrome (SIDS) and other causes. Notice the decrease since 1994 due to public interventions including the “back to sleep” campaign.
SUID: Sudden unexpected infact death

Image: “Trends in Sudden Unexpected Infant Death by Cause, 1990–2018” by CDC/NCHS, National Vital Statistics System, Compressed Mortality File. License: Public Domain, edited by Lecturio.

Etiology and Pathophysiology


The most likely cause of SIDS involves a multifactorial genesis in particularly vulnerable babies, in which internal and external factors work together.

  • Vulnerable infants: unable to detect or respond to hypoxia/hypercapnia 
    • Premature infants
    • Infants with brainstem abnormalities
    • Premature/low-birth-weight infants
    • Previous brief resolved unexplained event (BRUE)
  • Maternal risk factors
    • Maternal age younger than 20
    • Delayed prenatal care
    • Low socioeconomic status
    • Parental smoking
  • Environmental risk factors (many of these are modifiable risks)
    • Unsafe sleeping practices 
      • Allowing infant to sleep in prone position
      • Bed-sharing (co-sleeping)
      • Cluttered cribs (toys, pillows, blankets, etc.)
      • Using a soft sleeping surface
      • Covering infant’s head
    • Child abuse
    • Family history of SIDS
    • Overheating in a baby who sweats excessively


  • Thought to be a sequential process:
    1. Initial state of hypoxia 
    2. Progressive bradycardia
    3. Prolonged periods of apnea, and then suffocation
  • May be interrupted by external stimuli that prompt the infant to breathe
  • Changes in serotonin signaling in the brain may be involved.

Diagnosis and Management


SIDS is a diagnosis of exclusion that can be assigned only after:

  • A thorough examination of the scene and the circumstances surrounding the death
  • An autopsy that does not determine a medical cause of death
    • Always indicated in cases without an identifiable cause of death (in many countries and jurisdictions, this is legally mandatory)
    • Autopsy findings in SIDS may include:
      • Well-fed infant in good condition
      • No obvious signs of agitation or trauma (injuries, petechiae, ecchymosis)
      • Livor mortis found on the front of the body, but not on the face (due to prone position at the time of death)
      • Cyanotic lips and nail beds


The primary focus of management is providing an accurate post-mortem diagnosis as well as emotional and psychological support to the parents. Parents and family members should also be:

  • Allowed to spend time with the deceased infant
  • Offered grief counseling and closely monitored for signs of depression


Parental education is key to preventing SIDS. As noted above, many of the risk factors are modifiable and can be prevented. Parental education includes:

  • Encouraging regular prenatal care during pregnancy
  • Encouraging cessation of tobacco and illicit drugs
  • Safe sleeping practices
    • Infants should sleep supine (on backs) until 1 year of age.
    • Use a firm mattress.
    • Maintain an uncluttered crib (no stuffed animals, blankets, pillows, etc.).
    • Discourage co-sleeping (note that room-sharing is acceptable and may be a protective factor).
    • Discontinue swaddling when the infant can roll over.
    • Avoid overheating the infant/room.

Differential Diagnosis

The following conditions are natural causes of death to be distinguished from SIDS:

  • Respiratory infections in children (e.g., bronchiolitis, croup): can severely compromise oxygen intake and facilitate a state of apnea, with subsequent death if no intervention. 
  • Long QT syndrome: a disorder of myocardial repolarization characterized by a prolonged QT interval on electrocardiogram; associated with an increased risk of developing life-threatening arrhythmias, most notably torsades de pointes. Patients may be relatively asymptomatic at the time of death.
  • Inborn errors of fatty acid oxidation: Fatty acids are an important energy source for the infant, especially the newborn, as they are protective for brain tissue when glucose levels are low. Inborn errors of metabolism can cause a rapid depletion of energy stores.
  • Reye’s syndrome: an acute hepatic decompensation seen in children who have been given aspirin for temperature and symptom control during febrile illnesses.


  1. Szentpetery, S., Weiner, D. J., & Finder, J. D. (2018). Pulmonary disorders. In B. J. Zitelli MD et al.: Zitelli and Davis’ atlas of pediatric physical diagnosis (pp. 593-615).!/content/3-s2.0-B9780323393034000177
  2. Ferri, F. F., M.D. (2020). Shaken baby syndrome. In Ferri, Fred F., M.D., F.A.C.P. (Ed.), Ferri’s clinical advisor 2020 (pp. 1250.e4).!/content/3-s2.0-B9780323672542007993
  3. Madan-Khetarpal, S., & Arnold, G. (2018). Genetic disorders and dysmorphic conditions. In B. J. Zitelli MD, S. C. McIntire MD & Nowalk, Andrew J., MD, Ph.D. (Eds.), Zitelli and Davis’ atlas of pediatric physical diagnosis (pp. 1-43).!/content/3-s2.0-B9780323393034000013

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