Sudden Infant Death Syndrome (SIDS) is the sudden, unexpected and unexplained death of an infant. SIDS age range is from birth to 1 year of age

Sudden Unexpected Infant Death (SUID) is the sudden and unexpected infant death which may or may not be explained. SIDS is one type of SUID. You may also see SUID referred to as Sudden Unexpected Death in Infancy (SUDI).

How often does it occur?

In 2015, the United states lost 3700 infants from SUID. This includes 1600 from SIDS, and 900 deaths due to accidental suffocation and strangulation in bed. Most recent SIDS data still shows that SIDS is rare. There are about 40 infants lost to SIDS for every 100,000 live births.

View References

Centers for Disease Control and Prevention. Sudden unexpected infant death and sudden infant death syndrome. Available at https://www.cdc.gov/sids/data.htm Accessed 2/21/2018.

Why does it occur?

The truthful answer is we don’t know. We know that some infants seem to be more vulnerable to SIDS. SIDS tends to occur at certain stages of neurodevelopment. Also, SIDS is more likely with certain environmental exposures (like overheating or sleeping in any position other than on his/her back).

One leading model is considered the triple risk model, proposed by Filano and Kinney in 1994. This “triple risk model” suggests that SIDS occurs when multiple factors coincide.

In this model, SIDS occurs when a vulnerable infant is exposed to some environmental stressor during a critical stage in development.

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“Neuropathologic studies in SIDS victims support the concept that they are not entirely ‘normal’ prior to death, but rather possess underlying vulnerabilities which put them at risk for sudden death. This concept forms a key link in a triple-risk model for the pathogenesis of SIDS proposed by us. According to this model, sudden death in SIDS results from the intersection of three overlapping factors: (1) a vulnerable infant; (2) a critical developmental period in homeostatic control, and (3) an exogenous stressor(s). An infant will die of SIDS only if he/she possesses all three factors; the infant’s vulnerability lies latent until he/she enters the critical period and is subject to an exogenous stressor. According to this model, heterogeneous disorders may make the infant vulnerable to sudden death during the critical period, as potentially exemplified by two previously reported lesions in SIDS brains (arcuate nucleus hypoplasia and subtle hypomyelination). Nevertheless, the triple-risk model does not preclude the possibility that the majority of SIDS deaths will be explained by a single common pathway upon which multiple stressors impinge to produce sudden death during the critical period.”

View References

Reference: Filiano JJ, Kinney HC. A perspective on neuropathologic findings in victims of the sudden infant death syndrome: the triple-risk model. Biol Neonate. 1994;65(3-4):194–197

Who is at greater risk?

What causes this intrinsic vulnerability is unclear, but may be related to in-utero environmental conditions, genetics, development or delayed maturation.

In-utero environmental conditions:

  • Small for their gestational age (SGA) infants
  • Infants with prenatal cigarette or alcohol exposure
  • Twins (have about double the rate of SIDS compared to singleton births)


  • Random genetic mutations may increase the risk for SIDS. Genes involved in the immune system, heart, nerves, brain function and development have so far emerged as the most important with respect to SIDS.
  • Boys (XY) are at higher risk than girls (XX)
  • Siblings of SIDS victims are at higher risk, about 5-6x the rate of SIDS for the general population


  • Brain (dentate gyrus) and brainstem abnormalities were observed in up to 41% (dentate gyrus) and 70% (brainstem) of infants who die of SIDS
  • Preterm infants have 2-3x higher risk than term infants.
View References

Malloy MH, Freeman DH. Sudden infant death syndrome among twins. Arch Pediatr Adolesc Med. 1999;153(7):736.
Opdal GH, Rognum TO. Gene variants predisposing to SIDS: Current knowledge. Forensic Sci Med Pthol. 2011;7:26-36 Available from: www.researchgate.net/publication/45152301_Gene_variants_predisposing_to_SIDS_Current_knowledge [accessed Feb 09 2018].
Guntheroth WG, Lohmann R, Spiers PS. J Pediatr. 1990;116(4):520.
Beal SM, Blundell HK. Recurrence incidence of sudden infant death syndrome. Arch Dis Child. 1988;63(8):924.
Oyen N, Skjaerven R, Irgens LM. Population-based recurrence risk of sudden infant death syndrome compared with other infant and fetal deaths. Am J Epidemiol. 1996;144(3):300.
Carpenter RG, Waite A, Coombs RC, Daman-Willems C, McKenzie A, Huber J, Emery JL. Repeat sudden unexpected and unexplained infant deaths: natural or unnatural? Lancet. 2005;365(9453):29.
Kinney HC, Randall LL, Sleeper LA, et al. Serotonergic brainstem abnormalities in Northern Plains Indians with the sudden infant death syndrome. J Neuropathol Exp Neurol. 2003;62(11):1178–1191
Panigrahy A, Filiano J, Sleeper LA, et al. Decreased serotonergic receptor binding in rhombic lip-derived regions of the medulla oblongata in the sudden infant death syndrome. J Neuropathol Exp Neurol. 2000;59(5):377–384
Ozawa Y, Takashima S. Developmental neurotransmitter pathology in the brainstem of sudden infant death syndrome: a review and sleep position. Forensic Sci Int. 2002;130(suppl):S53–S59
Machaalani R, Say M, Waters KA. Serotoninergic receptor 1A in the sudden infant death syndrome brainstem medulla and associations with clinical risk factors. Acta Neuropathol. 2009;117(3):257–265
Kinney HC, Cryan JB, Haynes RL, et al. Dentate gyrus abnormalities in sudden unexplained death in infants: morphological marker of underlying brain vulnerability. Acta Neuropathol. 2015;129(1):65–80
Bigger HR, Silvestri JM, Shott S, Weese-Mayer DE. Influence of increased survival in very low birth weight, low birth weight, and normal birth weight infants on the incidence of sudden infant death syndrome in the United States: 1985-1991. J Pediatr. 1998;133(1):73-8.

There are racial and ethnic differences in sudden, unexpected infant death and SIDS.

View References

Copied from: Centers for Disease Control and Prevention. Sudden unexpected infant death and sudden infant death syndrome. Available at https://www.cdc.gov/sids/data.htm Accessed 2/21/2018.

What are the SIDS age ranges and distribution of the SIDS ages?

We know that SIDS Age peaks at age 1-4 months. In fact, about 72% of SIDS deaths occur during that time period, and 90% occur before 6 months of age. SIDS is rare after 8 months of age.

Modified From: Shapiro-Mendoza CK,
Tomashek KM et. al. Recent national trends in sudden unexpected infant deaths: more
evidence supporting a change in classification or reporting. American Journal of Epidemiology,
Volume 163, Issue 8, 15 April 2006, Pages 762–769. Available here:

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