Sudden infant death syndrome

Last updated: March 24, 2022

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Sudden infant death syndrome (SIDS) is the abrupt and unexplained death of an infant less than 1 year old. Although the etiology of SIDS remains unclear, evidence suggests that it is caused by a combination of environmental triggers and cardiorespiratory impairment, which then leads to prolonged hypoxia. Most SIDS cases occur in the first 6 months of life. Parents should receive information on how to prevent SIDS during prenatal care and in pediatric check-ups after birth: Recommendations include placing the infant on his/her back to sleep, ensuring a safe sleep environment, and avoiding overheating and second-hand smoke. SIDS is a diagnosis of exclusion; an autopsy is therefore important to rule out differential diagnoses (e.g., congenital cardiac anomalies or battered child syndrome).

Sudden infant death syndrome (SIDS) is the abrupt and unexplained death of an infant. Diagnosis requires that a forensic examination reveals no other cause of death.


  • Peak incidence: 2–6 months ; in rare cases, during the first days of life
  • Sex: >


Epidemiological data refers to the US, unless otherwise specified.

The etiology of SIDS remains unclear. Evidence suggests that it is caused by a combination of both extrinsic and intrinsic factors, which ultimately lead to acute or chronic hypoxia. Over 90% of cases of SIDS occur during sleep.

Extrinsic factors (triggers)

  • Sleeping in the prone position
  • Exposure to nicotine during pregnancy and after birth (including 2nd-hand smoking)
  • Overheating
  • Unsafe sleeping environment or CO2 rebreathing: e.g., a shared blanket, stuffed animals in the crib (because of the grasping reflex, newborns tend to drag items to their faces)
  • Many more correlations: SIDS in siblings, babies born prematurely, young mothers (< 20 years), low socioeconomic status, etc.

Intrinsic factors


SIDS is a diagnosis of exclusion. If there is an unexplained death of an apparently healthy infant, an autopsy is required by law to rule out other causes of death.

The differential diagnoses listed here are not exhaustive.

  • Definition: a sudden and unexpected event occurring in an infant that is considered life-threatening by the observer and is characterized by some combination of the following:
  • Epidemiology: reported incidence is 0.05–6%. [4]
  • Etiology
  • Clinical features
    • See “Definition.”
    • May occur while the infant is awake or asleep
    • Not associated with SIDS [5]
  • Prognosis: recurrence is high, but overall mortality is low (< 1%) [6]


Parents should receive information on how to prevent SIDS during prenatal care and in pediatric check-ups after birth.

  • During pregnancy
  • Protective factors after birth
    • The infant should be placed to sleep in the supine position
    • Safe sleep environment: firm mattress; no pillows, blankets, stuffed animals, or bumper pads in the crib.
    • In the first 6 months, co-sleeping in the same room without bed-sharing
    • Second-hand smoke and overheating should be avoided
    • Use of pacifier during sleep [8]
    • Breastfeeding until the 4th–6th month
    • "Tummy time"
    • Immunization in line with the official schedule


  1. Kinney HC, Thach BT. The Sudden Infant Death Syndrome. N Engl J Med. 2009; 361 (8): p.795-805. doi: 10.1056/nejmra0803836 . | Open in Read by QxMD
  2. Leach CEA, Blair PS, Fleming PJ, et al. Epidemiology of SIDS and explained sudden infant deaths. Pediatrics. 1999; 104 (4): p.e43-e43. doi: 10.1542/peds.104.4.e43 . | Open in Read by QxMD
  3. Kinney HC, Richerson GB, Dymecki SM, Darnall, Nattie EE. The brainstem and serotonin in the sudden infant death syndrome. Annu Rev Pathol. 2009; 4 : p.517-550. doi: 10.1146/annurev.pathol.4.110807.092322 . | Open in Read by QxMD
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  5. Hauck FR, Herman SM, Donovan M et al.. Sleep environment and the risk of sudden infant death syndrome in an urban population: the Chicago Infant Mortality Study. Pediatrics. 2003; 111 (5.2): p.1207-1214.
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  8. Alm B, Milerad J, Wennergren G. A case-control study of smoking and sudden infant death syndrome in the Scandinavian countries, 1992 to 1995. The Nordic Epidemiological SIDS Study.. Arch Dis Child.. 1998; 78 (4): p.329-334.
  9. Kandall SR, Gaines J, Habel L, Davidson G, Jessop D. Relationship of maternal substance abuse to subsequent sudden infant death syndrome in offspring. J Pediatr . 1993; 123 (1): p.120-126.
  10. Strandberg-Larsen K, Grønboek M, Andersen AM, Andersen PK, Olsen J. Alcohol drinking pattern during pregnancy and risk of infant mortality. Epidemiology. 2009; 20 (6): p.884-891. doi: 10.1097/EDE.0b013e3181bbd46c . | Open in Read by QxMD
  11. Hauck FR, Thompson JM, Tanabe KO, Moon RY, Vennemann MM. Breastfeeding and reduced risk of sudden infant death syndrome: a meta-analysis. Pediatrics. 2011; 128 (1): p.103-110. doi: 10.1542/peds.2010-3000 . | Open in Read by QxMD
  12. Hall KL, Zalman B. Evaluation and management of apparent life-threatening events in children.. Am Fam Physician. 2005; 71 (12): p.2301-8.
  13. Urquhart DS, Gahleitner F. Disorders of Respiratory Control in Childhood. Elsevier ; 2021
  14. Perlis ML, Gehrman P. Encyclopedia of Sleep. Academic Press ; 2013 : p. 199-202
  15. Horne RSC. Apparent Life Threatening Events (ALTE). Elsevier ; 2014 : p. 201-207

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