Sudden Infant Death Syndrome (SIDS)



  • Sudden infant death syndrome (SIDS) is the sudden and unexpected death of an infant <1 year of age, with onset of the lethal episode apparently occurring during sleep, which remains unexplained after a thorough investigation, including the performance of a complete autopsy, review of the circumstances of death, and review of the clinical history.
  • SIDS is a subcategory of deaths described as “sudden unexpected deaths in infancy” (SUDI) or “sudden unexpected infant deaths” (SUID). SUID can include both explained deaths, including suffocation, asphyxia, entrapment, trauma (accidental or nonaccidental), cardiac arrhythmia, infection, and metabolic disorders; and unexplained deaths, including SIDS and those with an undetermined/ill-defined cause of death.


  • Most common cause of death in postneonatal (1 month to 1 year old) infants
  • Peak age of incidence: 1 to 4 months; uncommon before 2 weeks or after 6 months
  • Incidence has been decreasing:
    • 1970s: ~2.5 SIDS deaths per 1,000 live births: SIDS defined somewhat loosely
    • 1980s: ~1.4 per 1,000 live births
    • 1990s: ~1.2 per 1,000 (1992) to 0.7 per 1,000 live births (1999): “Back to Sleep” campaign encouraging supine positioning during sleep in 1994 is associated with steady decline in deaths.
    • 2000s: Since 2001, SIDS rate has declined at a much slower rate. In 2013, the rate was 0.4 per 1,000 live births.
  • The rates of accidental suffocation and other undetermined or unspecified causes of death have risen.
    • For example, the death rate from accidental suffocation and strangulation in bed (ASSB) has increased 7-fold between 1994 and 2013.
    • Largely because of improved death scene investigations, many deaths that previously would have been classified as SIDS are now being classified as having resulted from these other causes of death.

Risk Factors

  • Male gender
  • Premature birth or low birth weight
  • Inadequate prenatal care
  • Poverty
  • Lower maternal educational level
  • Exposure to prenatal, gestational, and postnatal tobacco smoke
  • Alcohol and illicit drug use in utero and after infant’s birth
  • Maternal substance abuse
  • Young maternal age
  • Prone and side sleeping position
  • Overheating and overbundling
  • African American or American Indian/Alaska Native heritage
  • Soft sleep surface. Sofas, couches, and cushioned armchairs are particularly hazardous.
  • Soft and loose bedding
  • Bed sharing, particularly if sharing bed with one or more smokers; if the infant is <4 months of age (even if neither parent is a smoker); if the infant was born preterm or with low birth weight, if sleeping on a surface with soft bedding; if bed sharing adults have consumed alcohol or drugs; if bed sharing with people who are not the infant’s parents; and if the sleep surface is very soft (couches, armchairs, waterbeds)
  • Potential protective factors include the following:
    • Breastfeeding
    • Pacifier use at bedtime and naptime
    • Regular prenatal care
    • Immunizations
    • Room sharing without bed sharing


  • Most likely represents a heterogeneous group of causes of death
  • Genetic factors may play a role in some of these deaths. Candidate genes include those encoding ion channel proteins, serotonin transporters, nicotine-metabolizing enzymes, and those regulating autonomic nervous system development, inflammation, energy production, hypoglycemia, and thermal regulation.
  • There appears to be a complex gene and environment interaction.
  • Parents should be reassured that the chance of recurrence in future siblings is small and will be examined during the investigation of the SIDS death.

General Prevention

  • Place infants on their backs for every sleep until 1 year of life.
    • Preterm infants should be placed supine as soon as possible.
    • The supine sleep position does not increase the risk of aspiration and choking, even in infants with gastroesophageal reflux.
    • Elevating the head of the crib is not recommended as it may result in the infant sliding to the foot of the bed into a position that may comprise respiration.
    • Side positioning has similar risk as prone positioning and should be avoided.
  • Use a firm sleep surface.
  • Do not use blankets, pillows, bumper pads, sheepskins, or comforters in the infant’s sleep area.
  • Avoid tobacco smoke exposure during pregnancy and after birth.
  • Place the infant for sleep on a separate surface designed for infants in the parental room, close to the parental bed.
  • Breastfeed as much and as long as possible.
  • Consider offering a pacifier at naptime and bedtime. If breastfeeding, wait until breastfeeding is well established before introducing a pacifier. To decrease the risk of strangulation, do not use pacifiers that attach to infant clothing with sleeping infants.
  • Do not use alcohol or illicit drugs during pregnancy or after birth.
  • Avoid overheating.
  • Do not cover infant’s head during sleep.
  • Immunize your infant.
  • Do not use home cardiorespiratory monitors as a strategy to reduce the risk of SIDS.
  • Do not use commercial devices that are inconsistent with safe sleep recommendations.


  • The “triple risk” model of SIDS describes the interplay of three factors thought to contribute to these deaths: a vulnerable infant, a critical period of development, and stressful environmental challenges.
    • Individual traits that influence an infant’s vulnerability to SIDS are characterized as intrinsic risk factors. Examples include serotonin receptor abnormalities noted in the ventral medulla of up to 70% of SIDS infants at autopsy, suggesting derangements in the neural circuits responsible for arousal and cardiorespiratory functioning. Autopsy studies have also revealed changes in the serotonin transporter gene (5-HTT) that ultimately reduce serotonin concentration at these nerve synapses.
    • The period from birth to age 6 months is one of rapid brain growth and maturation, as well as motor skill acquisition, such as the ability to lift and turn the head in the event of life-threatening rebreathing or asphyxia.
    • Exogenous risk factors such as soft bedding, tobacco smoke, side or prone positioning, and overheating place these vulnerable infants at risk for asphyxia or other physiologic disturbances.
  • Failure of arousal in the face of asphyxia or other physiologic disturbances likely contributes to the final pathway leading to these infants’ deaths. Known risk factors for SIDS have been linked to arousal and cardiorespiratory responses; for example:
    • Prematurely born infants have immature central respiratory responses.
    • When compared with supine-sleeping infants, prone-sleeping infants have increased arousal thresholds.
    • Prenatal and postnatal nicotine exposure blunts arousal responses to hypoxia.

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