Background Content

Sudden Unexpected Deaths in Infancy

• Sudden unexpected death in infancy refers to the unexpected death of an infant who was thought to be healthy. Unexpected deaths are often thoroughly investigated and sometimes a cause is found. In many cases, however, a cause is not determined.
• SIDS is defined as the sudden death of an infant less than one year of age that remains unexplained after a thorough case investigation, including examination of the death scene, completion of an autopsy, and review of the clinical history. It is generally understood that death occurs during sleep.
• SIDS is one of the most important causes of death in the first year of life, accounting for approximately 30% of post-neonatal deaths occurring between one month and one year of age.
• In Canada, SIDS accounts for the deaths of approximately 35 infants per 100,000 live births each year.
• The peak incidence of SIDS occurs between two and four months of age.
• The risk for SIDS is greatest between one and six months of age with 90% of SIDS cases occurring in infants of this age group.
• The acronym SIDS and the term sudden unexpected deaths are used interchangeably.

Risk Factors for Sudden Unexpected Deaths in Infants

• A cause is not found in many cases of sudden unexpected death in infants. Studies have identified associated risk factors including weather – i.e. increased risk during winter months, or infants who are born prematurely, male, prone sleeping position, and whose mothers smoked tobacco during or after pregnancy.
• It is important to note that risk factors are not causes. The presence of risk factors may increase the risk of unexpected death in infants, but the factors are not, in themselves, the cause of death.

Death by Asphyxia versus Unexplained Death

• Two types of deaths can occur in a sleeping environment perceived as unsafe: death by asphyxia (an unintentional injury) and unexplained death.
• Asphyxia is identified as the cause of death when: an infant is discovered with airways obstructed by an object or a person’s body, and access to fresh air is not possible. An infant is discovered trapped in a restricted space without access to fresh air or an infant is strangled by an object (e.g. a blind cord in a crib that is next to a window with a window treatment).
• Deaths by asphyxia are not classified as sudden unexplained deaths. Avoidance of unsafe sleeping environments could have prevented these deaths.
• A sudden unexpected death in an unsafe sleeping environment is considered “unexplained” when the deceased infant is found with no obvious obstruction of the airways. These deaths are due to either an as yet unidentified cause (totally unexplained deaths) or asphyxia in the sleeping environment but with no way to confirm this.