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Sudden Infant Death Syndrome (SIDS)

By Christopher P. Raab, MD, Associate Professor of Pediatrics;Attending Physician, Diagnostic Referral Division, Sidney Kimmel Medical College at Thomas Jefferson University;Nemours/Alfred I. duPont Hospital for Children

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Sudden infant death syndrome is the sudden and unexpected death of an infant or young child between 2 wk and 1 yr of age in which an examination of the death scene, thorough postmortem examination, and clinical history fail to show cause.

Sudden infant death syndrome (SIDS) is the most common cause of death of infants between 2 wk and 1 yr of age, accounting for 35 to 55% of all deaths in this age group. The rate of SIDS occurrence is 0.5/1000 births in the US; there are racial and ethnic disparities (African American and Native American children have twice the average risk of SIDS). Peak incidence is between the 2nd and 4th mo of life. Almost all SIDS deaths occur when the infant is thought to be sleeping.


The cause of SIDS is unknown, although it is most likely due to dysfunction of neural cardiorespiratory control mechanisms. The dysfunction may be intermittent or transient, and multiple mechanisms are probably involved. Factors that may be involved are the infant having a poor sleep arousal mechanism, an inability to detect elevated CO2 levels in the blood, or a cardiac channelopathy that affects heart rhythm.

Fewer than 5% of infants with SIDS have episodes of prolonged apnea before their death, so the overlap between the SIDS population and infants with recurrent prolonged apnea is very small.

Risk factors for SIDS

The association between a prone (on stomach) sleeping position and an increased risk of SIDS has been documented strongly.

Other risk factors (see Table: Risk Factors for Sudden Infant Death Syndrome) include old or unsafe cribs, soft bedding (eg, lamb’s wool), waterbed mattresses, bed-sharing with a parent/caregiver, smoking in the home, and an overheated environment. Siblings of infants who die of SIDS are 5 times more likely to die of SIDS; it is not clear whether this is related to genetics or environment (including possible abuse by the affected infant's family).

Many risk factors for SIDS apply to non-SIDS infant deaths as well.

Risk Factors for Sudden Infant Death Syndrome

African American or Native American ethnicity

Bed-sharing with parent/caregiver

Cold temperatures/winter months

Episodes of apnea requiring resuscitation

Growth failure

Increased parity

Low birth weight

Lower socioeconomic group

Male sex

Maternal age <20 yr

Maternal drug use during pregnancy

Maternal smoking during pregnancy

No pacifier

Old or unsafe cribs

Overheating (eg, blankets, hot room)

Poor prenatal care

Prone sleeping position*

Recent illness

Short interval between pregnancies

Sibling of a SIDS victim

Smoking in the home

Soft bedding

Waterbed mattress

*Most important.


  • Exclusion of other causes by autopsy

The diagnosis of SIDS, while largely one of exclusion, cannot be made without an adequate autopsy to rule out other causes of sudden, unexpected death (eg, intracranial hemorrhage, meningitis, myocarditis). An autopsy may be required in many states. Also, the care team (including social workers) should sensitively assess the likelihood of infant suffocation or nonaccidental trauma; concern for this etiology should increase when the affected infant was outside the highest-risk age group (1 to 5 mo) or another infant in the family had SIDS or frequent apparent life-threatening events.


Parents who have lost a child to SIDS are grief-stricken and unprepared for the tragedy. Because no definitive cause can be found for their child’s death, they usually have excessive guilt feelings, which may be aggravated by investigations conducted by police, social workers, or others. Family members require support not only during the days immediately after the infant’s death but for at least several months to help them with their grief and dispel guilt feelings. Such support includes, whenever possible, an immediate home visit to observe the circumstances in which SIDS occurred and to inform and counsel the parents concerning the cause of death.

Autopsy should be done quickly. As soon as the preliminary results are known (usually within 12 h), they should be communicated to the parents. Some clinicians advise a series of home or office visits over the first month to continue the earlier discussions, answer questions, and give the family the final (microscopic) autopsy results. At the last meeting, it is appropriate to discuss the parents’ adjustment to their loss, especially their attitude toward having other children. Much of the counseling and support can be complemented by specially trained nurses or by lay people who have themselves experienced the tragedy of and adjustment to SIDS (visit for more information and resources).


The American Academy of Pediatrics (see SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment) recommends that infants be placed supine (on their back—see the Safe to Sleep® campaign) for sleep unless other medical conditions prevent this. Side sleeping or propping is too unstable. The incidence of SIDS increases with overheating (eg, clothing, blankets, hot room) and in cold weather. Thus, every effort should be made to avoid an overly hot or an overly cold environment, to avoid overwrapping the infant, and to remove soft bedding, such as sheepskin, pillows, stuffed toys/animals, and comforters, from the crib. Pacifiers may be helpful, because they help open the airway. Parents/caregivers should not have the infant sleep in their bed.

Mothers should avoid smoking during pregnancy, and infants should not be exposed to smoke. Breastfeeding is encouraged to help prevent infections. There is no evidence that home apnea monitors reduce the incidence of SIDS and therefore are not suggested for prevention.

Key Points

  • Specific causes, including child abuse, must be ruled out by clinical evaluation and autopsy.

  • Etiology is unclear, although a number of risk factors have been identified.

  • The most important modifiable risk factors involve the sleep setting, particularly prone sleeping, along with bed-sharing and sleeping on very soft surfaces or with loose bedding.

  • Apneic episodes and apparent life-threatening events (ALTEs) do not appear to be risk factors.

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