One of the greatest challenges the DU5C reviewers face is trying to properly assign manner and cause of death. The most challenging cases are in children less than one year of age, where the autopsy has not clearly demonstrated a cause of death. Even with the most qualified and experienced forensic pathologists performing the autopsy, it is not uncommon for the cause of death to be undetermined.

Learning more about sudden and unexpected infant deaths and advancing our findings continues to be a priority for Ontario’s death investigation system with regular discussion about the approach to death investigation, and specifically, post mortem examination at the time of a sudden and unexpected infant death.

The Ontario Forensic Pathology Service (OFPS) adheres to scientifically informed guidelines that forensic pathologists follow when they complete these examinations at regional forensic pathology units.  Ancillary testing includes: extensive histology; microbiologic evaluation; toxicologic analysis and detailed metabolic analysis. Additional testing and expert evaluation are completed when required and DNA is routinely isolated and retained. 

In recent years molecular testing has not been completed in all cases of sudden and unexpected infant death.  While testing was considered in unexpected infant deaths, there was concern that if testing identified abnormalities of unknown significance relating to the death, reporting the abnormality could lead to undue concern for surviving and future family members.  It was felt that clinicians were in the best position, based upon their clinical assessment of family members, to determine the most appropriate testing.

There have been significant advances in the area of molecular testing over recent years including in the area of unexpected infant deaths.  Ontario’s death investigation system has continued to work closely with paediatric cardiologists and geneticists who have expertise in evaluating heritable cardiac abnormalities.  Consultation with these experts has informed the development of a protocol for molecular testing in all cases of unexpected infant deaths where the post mortem examination has not identified a cause of death.  

The classification of infant deaths continues to be a topic of discussion for the death investigation field. Different death investigations, including Canadian provincial and territorial jurisdictions, use their own approaches in the classification of infant deaths. Consistent use of definitions and terminology is important to ensure clear understanding and effective classification of sudden and unexpected infant deaths.

One of the significant changes reflected in the classification of these deaths (see Chart 10) involves the cause of death being provided as “undetermined” in cases where there is a comprehensive investigation but no conclusive finding. Previously, based upon a 2005 publication of the National Association of Medical Examiners, many death investigation jurisdictions use the often confusing “Sudden Unexpected/Unexplained Death in Infancy (SUDI)” on the Medical Certificate of Death. This terminology is not used by the DU5C.

Chart 10 identifies the criteria used for classifying infant deaths in Ontario.

Chart 10: Infant Death Classification

Chart 10
CaseAutopsy findingsInvestigative findingsCause of death on death certificateManner of death
1Autopsy reveals a definitive cause of death (pneumonia, head injury, etc.) that informs a definitive manner of deathVariable/may directly inform cause/manner of deathAs per the autopsy/investigative findingsBased on autopsy/ circumstances
2 (category 2 - see below)No anatomic or toxicologic cause of death identifiedNo findings of concern identified during the complete investigation

- child found supine or prone

- no evidence of sleep associated circumstances (see below)

- may include exposure to environmental tobacco smoke or in utero tobacco use 
Ia- Sudden Infant Death Syndrome (SIDS)Natural
3ANo anatomic or toxicologic cause of death identifiedPresence of sleep associated circumstances (see below)

Presence or absence of social risk factors (see below)
Ia- Undetermined


II-Unsafe Sleep

Environment (description in parentheses)
3BNo anatomic or toxicologic cause of death identifiedIncludes cases that do not meet definition of SIDS

No sleep associated circumstances (see below)

May be presence of social risk factors (see below)
Ia- Undetermined


4No anatomic or toxicologic cause of death identifiedFindings in investigation/ autopsy, examples include: - autopsy findings for which the differential diagnosis includes non- accidental injury (eg: healing fracture, bruises, etc.)

- death of a previous child in suspicious circumstances

- significant toxicologic findings for which there is an inadequate explanation
Ia- Undetermined


II- Multiple healing
rib fractures

Sleep associated circumstances include:

  • Sharing a sleep surface with a person or pet (adult, toddler, child, cat, dog, etc.)
  • Sleeping on a surface not intended for infant sleep (adult bed, waterbed, sofa, child carrier, car seat, non-approved playpen or bassinet)
  • Sleeping in a cluttered sleep environment (bedding, toys, clutter in the sleep area that represent an asphyxia potential)

Social risk factors, including, but not limited to:

  • Previous involvement with child welfare agencies, substantial mental health histories in caregivers, domestic violence in the home, alcohol or substance use in the caregivers, concerning, but non- specific investigative findings (for example, inconsistent accounts of circumstances surrounding the death)
  • these risk factors will not be listed on the Medical Certificate of Death.

Category 2 represents deaths that meet the definition of Sudden Infant Death Syndrome (SIDS)

As defined: Sudden death of an infant under 1 year of age that remains unexplained after a thorough case investigation, which must include:

  • A complete autopsy
  • (including full skeletal survey & toxicology)
  • Review of the circumstances of death
  • Examination of the death scene
  • Police investigation
  • Review of the clinical history

A death will not be considered in Category 2 (SIDS definition is not met) if any of the following is/are present:

  • Presence of sleep associated circumstances (described above):
  • Presence of social risk factors (described above)
  • Anatomic or toxicologic findings that do not establish a cause of death, but for which the differential diagnosis includes maltreatment, and the caregiver has no explanation for the findings, or the caregiver’s explanation for the findings is unwitnessed, or undocumented

A death would be considered as Category 4 if:

  • Anatomic or toxicologic findings are present that do not establish a cause of death, but for which the differential diagnosis includes non-accidental injury, and the caregiver’s explanation of these findings are unwitnessed or undocumented.