What is SIDS?
SIDS, or Sudden Infant Death Syndrome, is the unexplained death of an infant under 1 year of age.  It is a diagnosis of exclusion, meaning every possible cause of death has been ruled out before using a diagnosis of SIDS.

SIDS is the 3rd leading cause of infant death behind birth defects and preterm birth/low birth weight.

In the last several years, the terms used for a sudden infant death have become confusing, not only to parents, but also to professionals and researchers.  Other terms that might be used with an unexpected infant death include SUID, SUDI, positional asphyxia, or accidental strangulation in bed (ASSB). 

Terms used for sleep-related unexpected infant deaths:
CDC (Centers for Disease Control), in an attempt to clarify the terminology issue, suggested that SUID (Sudden Unexpected Infant Death) be used as a broad term that encompasses all sudden infant deaths. This would include SIDS as well as other accidental deaths (such as suffocation and strangulation), and sudden natural deaths (such as those caused from infections, cardiac or metabolic disorders, and neurological conditions), and homicides. You might also see SUDI (sudden unexplained death in infancy) that is used in a similar way. 

Some others however, use SUID to mean Sudden Unexplained Infant Death. For example when a medical examiner, even after a thorough scene investigation, cannot tell the difference between SIDS and suffocation, they will often use this term to mean it is unexplained. Other medical examiners might call these “undetermined” or list the cause of death as "unknown" and others would still call them SIDS.

In the cases of positional asphyxia or accidental strangulation, there is often no clear physical evidence of an airway compromise that led to the death.  Since by autopsy alone, there is usually no way to tell the difference between suffocation and SIDS, the scene investigation is of utmost importance. Increasingly, investigators are using doll reenactments at the home to help parents clarify the situation surrounding their infant’s death.  If there were potentially asphyxiating environmental factors, it is up to the medical examiner as to whether that will be listed as the cause of death.  Deaths that would have been named as SIDS deaths in decades past are often being assigned as positional asphyxia or accidental strangulation today. In short, the conclusion that the death is caused by a lethal asphyxiating environment is based on circumstantial evidence of variable degrees of certainty. 

There are about 4,000 sudden infant deaths a year in the US. About ½ of these are diagnosed as SIDS or unexplained and the other ½ are diagnosed as due to other causes. Our mission includes all those who have experienced an unexpected infant death.

1. http://www.cdc.gov/SIDS/
2. http://sids.org
3. Assigning Cause for Sudden Unexpected Infant Death