Sudden Infant Death Syndrome


  • Leading cause of death in infants 1 to 12 months of age
  • Third leading cause of infant mortality overall
  • Sudden infant death syndrome (SIDS) deaths have been reduced by >50% in the United States and other countries that have introduced risk-reduction campaigns, heavily focused on back sleeping for infants.
  • The exact cause remains unknown, although a great deal of progress has been made in understanding the possible underlying pathophysiology.


  • The sudden death of an infant <1 year of age 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
  • SIDS was first formally defined in 1969. The definition was revised in 1989.
  • In past 20 years, there has been a shift in classifying sleep-related deaths as accidental suffocation and asphyxia in bed or unknown cause rather than SIDS, which has created increased confusion about how to define and study these deaths. Several classification systems have been proposed that attempt to address this problem (1).
  • System(s) affected: cardiovascular, endocrine/metabolic, nervous, pulmonary
  • Synonym(s): crib death; cot death


  • SIDS can affect any infant, but some infants are at higher risk than others, including African Americans and American Indians/Native Americans, males, infants whose mothers smoked/used illegal drugs during pregnancy, and several others described below.
  • There is a characteristic age pattern, with deaths peaking at 2 to 4 months, and more deaths occurring during the colder seasons.


  • For 2015: all races: 0.39/1,000 live births (1,568 cases per year)
    • White non-Hispanic: 0.36/1,000 live births (771 cases per year)
    • African American non-Hispanic: 0.87/1,000 live births (513 cases per year)
    • Hispanic: 0.22/1,000 live births (202 cases per year)
    • Native American: 1.33/1,000 live births (49 cases per year)
    • Asian/Pacific Islander: 0.09/1,000 live births (25 cases per year)
  • Predominant age: uncommon in 1st month of life; peak occurs between 2 and 4 months of age; 90% of deaths occur by 6 months of age.
  • Predominant sex: male > female (52–60% male)

Pediatric Considerations
Occurs only in infants

Etiology and Pathophysiology

Strong evidence for a respiratory pathway that includes the following stages:

  • A life-threatening event causes severe asphyxia and/or brain hypoperfusion. This can include rebreathing exhaled carbon dioxide in a facedown position.
  • The vulnerable infant does not wake up or turn his or her head in response to asphyxia, resulting in further rebreathing and inability to recover from apnea.
  • Progressive apnea leads to hypoxic coma.
  • Bradycardia and hypoxic apnea occur.
  • Autoresuscitation fails, resulting in prolonged apnea and death.
  • There are many theories to explain why some infants are more vulnerable to this pathway than others. There may be subtle developmental abnormalities resulting from pre- and/or perinatal brain injury.
  • Possible causes
    • Abnormalities in respiratory control and arousal responsiveness
    • Central and peripheral nervous system abnormalities
    • Cardiac arrhythmias
    • Rebreathing in facedown position on soft surface, leading to hypoxia and hypercarbia
    • SIDS may occur when ≥1 environmental risk factors interact with ≥1 genetic risk factors.

Emerging evidence for genetic risk factors, especially related to impaired brainstem regulation of breathing or other autonomic control, impaired immune responses, and cardiac ion channelopathies associated with long QT syndrome and fatal arrhythmia

Risk Factors

  • Although some infants may die from SIDS who have no apparent risk factors, most have ≥1 of the following risk factors associated with SIDS:
    • Race: African Americans and Native Americans have highest incidence.
    • Season: late fall and winter months
    • Time of day: between midnight and 6 AM
    • Activity: during sleep
    • Low birth weight; preterm birth; intrauterine growth retardation
    • Poverty
  • Maternal factors
    • Younger age
    • Decreased education
    • Maternal use of cigarettes/drugs (e.g., cocaine, opiates) during pregnancy
    • Higher parity
    • Inadequate prenatal care
  • Respiratory/GI infection in recent past
  • Sleep practices
    • Prone and side sleep positions
    • Overheating from heavy clothing and bedding and/or elevated room temperature
    • Soft bedding
    • Bed sharing, independent of other factors
    • Parental smoking, alcohol, and drug use greatly increase the risk associated with bed sharing.
    • Sleeping in a room other than the parents’ room
  • Passive cigarette smoke exposure after birth
  • Not breastfeeding; not using pacifier
  • Swaddling is associated with a small increase in SIDS risk; this risk increases greatly when sleeping prone (2)[B].

General Prevention

Because a SIDS death is sudden and the cause is unknown, SIDS cannot be “treated.” However, some measures may be effective in reducing the risk of SIDS (3)[B]:
  • Maternal avoidance of cigarette smoking and illicit drug use during pregnancy
  • Avoidance of passive cigarette smoke exposure
  • Avoidance of the prone (facedown) and side sleep positions, excessive bed clothing, and soft bedding such as pillows, comforters, and bumper pads or a soft mattress. Bumper pads of any kind are not recommended.
  • Avoidance of overheating
  • A crib, bassinet, or cradle conforming to federal safety standards is the recommended sleeping location. Crib mattresses should also conform to federal safety standards.
  • Avoidance of bed sharing (sharing the same sleep surface) with the infant, particularly by adults other than the parent(s) or by other children. Bed sharing should be avoided if the mother/father has used cigarettes, drugs, or alcohol. Bed sharing on couches or chairs is very dangerous and should never be done.
  • Infants who sleep in the same room as their parents (without bed sharing) have a lower risk of SIDS. It is recommended that infants sleep in a crib/bassinet in their parents’ bedroom, for at least the first 6 months of life, which when placed close to their bed will allow for more convenient breastfeeding and contact.
  • Breastfeeding is associated with a decreased risk of SIDS and is recommended for all infants (4)[B].
  • Pacifier use is associated with a reduced risk of SIDS.
    • Consider offering a pacifier at bedtime and nap time.
  • Avoid commercial devices marketed to reduce the risk of SIDS.
  • It is critical that all people caring for infants, including daycare providers, be instructed in these risk-reduction measures.
  • Newborn nurseries should implement these recommendations well before discharge, so parents see appropriate practices modeled.
  • The guidelines related to safe infant sleep environment are also effective in reducing the risk of other sleep-related infant deaths.

Commonly Associated Conditions

Infants are generally well or may have had a mild febrile illness (i.e., gastroenteritis or an upper respiratory infection) prior to death.

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