Sudden Infant Death Syndrome- SIDS


The Sudden Infant Death Syndrome (SIDS) definition:

the sudden death of an infant under twelve months old, which remains unexplained after a thorough case investigation including performance of an autopsy, examination of the death scene and review of clinical history [1].  



In the United States, SIDS is the third leading cause of infant mortality overall and the most common cause of death in infants one month to one year of age [2].  Approximately 2,300 deaths per year are attributed to SIDS in the US. 


The incidence of SIDS in the US decreased by approximately 50% from 1994 to 2000 following the introduction of the “Back to Sleep” campaign.  However, since 2001 the rate of SIDS remained constant.   Other forms of explained sudden infant death, including asphyxiation, increased over the same period.  



A few more facts about SIDS are:

  1. 95% of infants are < 6 months old. 85% are between 2-4 months of age
  2. The incidence is higher in Native Americans > African Americans > Caucasians > Asians
  3. Incidence is highest in winter.



The underlying cause of SIDS remains undetermined, with a multifactorial underlying etiology.  Apnea once formed the prevailing hypothesis regarding the cause of SIDS; however studies demonstrating infants succumbing to SIDS experienced fewer apneic events compared to infants surviving to childhood weakened support for this hypothesis [3].   

Currently, brainstem deficits leading to a diminished response to hypercarbia, hypoxia and hypothermia is considered one of the leading hypotheses regarding the underlying etiology of SIDS [4].  

Evidence of ethnic disparities in SIDS rates led to the investigation of various underlying genetic causes.   Current research focuses on genetic abnormalities of the serotonergic system, including the serotonin transporter gene SLC6A4 or 5-HTT.  Other genetic investigations focus on the autonomic nervous system, nicotine-metabolizing enzymes, ion channel proteins, inflammatory regulators, energy production, hypoglycemia, and thermal regulation [4].    


Risk Factors

The risk of SIDS is increased in male infants at a ratio of approximately 3:2 [2].  Prone and side sleeping increases the risk of SIDS.  African Americans and American Indian/Alaska Native heritage carries an increased risk. 

Other risk factors include maternal smoking during pregnancy and exposure to environmental tobacco smoke, overheating, soft bedding, inadequate prenatal care, young maternal age, prematurity or low birth weight, and a if a sibling died from SIDS



SIDS remains, by definition, a diagnosis of exclusion.  

However, certain features at autopsy are consistent with SIDS, including: 

  • Encephalomegaly, pulmonary edema, intrathoracic petechiae, microcardia, reduced kidney size, unclotted blood in the heart, and an empty bladder and rectum and findigs consistent with chronic hypoxia [4].   


Risk Reduction

Following the success of the Back to Sleep campaign in 1992, the American Academy of Pediatrics issued a policy statement in 2011 highlighting methods to reduce the incidence of SIDS [5].  

The recommendations consist of the following:


Supine sleep positionInfants should be placed in the supine position by the caregiver for every sleep until reaching one year of life.   The supine position is not associated with an increased risk of aspiration, and is still recommended in infants with gastroesophageal reflux.  Side sleeping similarly carries an increased risk of SIDS and is not recommended. 


Use of a firm sleep surface:  The AAP recommends use of a firm crib mattress covered by a fitted sheet.  The mattress should extend to the side of the crib without gaps.  Pillows and other soft materials such as quilts, comforters or cushions should not replace a mattress, or be used on top of a mattress, even when covered in a fitted sheet.  Infants should not be placed in beds due to the risk of suffocation.   Other hazards, such as dangling cords or electrical wires, should be cleared from the area.  Other safety devices, such as strollers, slings, car seats or carriers should not be used for routine sleep, due to the lack of a stable surface. 


Room sharing without bed sharingAvoidance of sleep in an adult bed reduces the risk of accidental suffocation or entrapment.  Sleeping in a crib in the same room as the caregiver facilitates feeding, comforting and monitoring of the infant.   There are no recommended measures to make bed sharing safe.  Twins require separate sleeping areas and should not co-sleep in the same crib. 


Crib objects:  The crib should remain clear of soft objects and loose bedding, such as pillows, toys, or comforters. 


Prenatal care:  Regular prenatal care is recommended due to an association with a decreased risk of SIDS. 


Smoke and other drug exposures:  Avoidance of smoke exposure is recommended both during pregnancy and after birth due to a decreased risk of SIDS.   Similarly, avoidance of alcohol and illicit drugs during and after pregnancy is recommended. 


Breastfeeding:  Breastfeeding is associated with a lower risk of SIDS.  While fully breastfed infants experience the greatest protective effect, partially breast fed infants are also at lower risk of SIDS. 


Pacifier use at nap and bedtime:  The use of pacifiers appears to provide a protective effect against SIDS.  The protective effect appears to continue even after a pacifier falls out from the infant’s mouth, and need not be reinserted during sleep.   The pacifier should not be hung around the infant’s neck or attached to other objects that could pose a risk of strangulation. 


Overheating:  Studies demonstrate an increased risk of SIDS with overheating, thus infants should be assessed for signs of overheating such as sweating or feeling hot to the touch.   There is currently insufficient evidence to suggest a benefit to use of a fan in reducing the risk of SIDS.   


Tummy time:  Supervised, awake time spent in the prone position aids in prevention of positional skull deformities and promotes development of upper body muscles. 


Additional measures:  The AAP guidelines also suggested the avoidance of commercial products marketed to prevent SIDS, as there is insufficient evidence to show these items provide a protective effect against SIDS.  The use of home cardiorespiratory monitors to prevent SIDS is similarly lacking in evidence to demonstrate a protective effect.  Health care professionals should promote SIDS risk-reduction recommendations.  Media and manufactures should follow safe-sleeping guidelines in their marketing of products.  The guidelines promote expansion of the national campaign for SIDS prevention and continued research into reducing the risk of SIDS. 


Management of Sudden Infant Death

  1. There are few things more devastating to a family than the sudden unexpected death of an infant. It is important for the pediatrician to be in contact with the family soon after the event to obtain a thorough history and permission for an autopsy. It is imperative that the death scene is investigated. Avoid accusations.
  2. As soon as the autopsy results are known, the parents must be informed of the findings
  3. 4-6 weeks after the death, the parents should visit the pediatrician to discuss any questions that the family may have.
  4. The parents and family can be directed to organizations that are available for parents of SIDS victims. Not all parents are interested in joining groups, so do not force this upon them. The link below is to one such type of support organization.


  1. If the mother becomes pregnant again, make yourself available for questions. In addition, after the birth of the next child, be prepared for the mother to be very anxious until the high incidence periods of SIDS has passed or until the new infant live past the time the previous child died. The family may request a monitor, sleep/apnea studies, refuse immunizations, and call often. Be patient.



  1. Willinger M et al.  Defining the sudden infant death syndrome (SIDS): Deliberations of an expert panel convened by the National Institute of Child Health and Human Development. Pediatr Pathol 11:677-684, 1991
  2. Moon RY et al.  Sudden Infant Death Syndrome: An Update.  Pediatrics in Review 2012;33;314 DOI: 10.1542/pir.33-7-314
  3. Schechtman VL et al.  Sleep apnea in infants who succumb to the sudden infant death syndrome. Pediatrics 87:841-846, 1991
  4. Rand CM et al.  Congenital central hypoventilation syndrome and sudden infant death syndrome: disorders of autonomic regulation.  Semin Pediatr Neurol.   2013 Mar;20(1):44-55. doi: 10.1016/j.spen.2013.01.005.
  5. Task Force on Sudden Infant Death Syndrome. Policy Statement: SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment.  Pediatrics 2011; 128:5 1030-1039; published ahead of print October 17, 2011, doi:10.1542/peds.2011-2284


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