What is Sudden Infant Death Syndrome (SIDS)?

Sudden Infant Death Syndrome (SIDS)

Sudden Infant Death Syndrome (SIDS) is a cause assigned to infant deaths that cannot be explained after a thorough case investigation including a scene investigation, autopsy, and review of the clinical history. 1

Definition and Classification

SIDS is a subcategory of Sudden Unexpected Infant Death (SUID), which is a broader term used to describe any sudden and unexpected death occurring during infancy. After investigation, SUIDs can be attributed to various causes including:

• Suffocation
• Asphyxia
• Entrapment
• Infection
• Ingestions
• Metabolic diseases
• Trauma (accidental or nonaccidental)
• Arrhythmia-associated cardiac channelopathies 1

When these specific causes are ruled out through thorough investigation, the death may be classified as SIDS.

Diagnostic Process

The diagnosis of SIDS requires:

• Complete autopsy
• Death scene investigation
• Review of clinical history 1

Without these elements, a death cannot be properly classified as SIDS. In the United States, the National Center for Health Statistics assigns a SIDS diagnostic code (ICD-10 R95) when the death certificate includes terminology such as:

• SIDS (including presumed, probable, or consistent with SIDS)
• Sudden infant death
• Sudden unexplained death in infancy
• Sudden unexpected infant death 1

Epidemiology

Key epidemiological facts about SIDS include:

• Peak mortality occurs at approximately 3 months of age 2
• The US SIDS rate declined from 120 deaths per 100,000 live births in 1992 to 56 deaths per 100,000 live births in 2001, representing a 53% decrease over 10 years 1
• The rate has plateaued since 2001 1
• Significant racial and ethnic disparities exist, with non-Hispanic Black and American Indian/Alaska Native infants having more than double the SUID rate compared to non-Hispanic white infants 1

Risk Factors

The most significant risk factors for SIDS relate to the sleep environment:

Sleep Position

• Prone (stomach) and side sleeping positions are significantly more dangerous than the supine (back) position 3

Sleep Environment

• Bed-sharing, especially with infants younger than 12 weeks 3
• Soft bedding, pillows, or loose objects in the sleep area 1
• Overheating due to overbundling 1

Other Risk Factors

• Exposure to tobacco smoke during pregnancy and after birth 1
• Alcohol and illicit drug use during pregnancy and after birth 1
• Prematurity and low birth weight
• Male sex 2
• Multiple births (twins) 2
• Young maternal age 2

Prevention Strategies

The American Academy of Pediatrics recommends the following measures to reduce the risk of SIDS:

Level A Recommendations (Strongest Evidence)

• Back to sleep for every sleep
• Use a firm sleep surface
• Room-sharing without bed-sharing
• Keep soft objects and loose bedding out of the crib
• Avoid smoke exposure during pregnancy and after birth
• Avoid alcohol and illicit drug use during pregnancy and after birth
• Breastfeeding
• Consider offering a pacifier at nap time and bedtime
• Avoid overheating 1

Level B Recommendations

• Ensure infants are immunized according to recommendations
• Avoid commercial devices marketed to reduce SIDS risk
• Provide supervised, awake tummy time to facilitate development 1

Pathophysiology

The exact cause of SIDS remains unknown, but current understanding suggests a multifactorial condition involving:

1. A vulnerable infant (possibly due to genetic, developmental, or metabolic factors)
2. A critical developmental period
3. Environmental stressors 4

This is often referred to as the "triple-risk model" of SIDS. Recent research has focused on brainstem abnormalities that may affect arousal, cardiorespiratory control, and autonomic regulation during sleep 4, 5.

Important Considerations

• SIDS is distinct from apparent life-threatening events (ALTEs), which are not considered risk factors for SIDS 3
• The Back to Sleep campaign (now Safe to Sleep) has been credited with reducing SIDS rates by more than 50% 3
• One consequence of the Back to Sleep campaign has been an increase in occipital flattening (positional plagiocephaly), which can be addressed by alternating the infant's head position during sleep 3
• Despite prevention efforts, SIDS remains a leading cause of infant mortality worldwide 5

Understanding SIDS requires a multidisciplinary approach involving pathologists, pediatricians, microbiologists, and other specialists to thoroughly investigate each case and continue advancing our knowledge of this devastating condition.