Forty per cent SIDS, thirty-two per cent unknown, twenty-eight per cent suffocation

Sudden unexpected infant death (SUID) is an umbrella, not a diagnosis. It
covers three separate classifications:

• SIDS — sudden infant death syndrome
• Unknown cause
• ASSB — accidental suffocation and strangulation in bed

The 2024 split

Three roughly comparable slices, and the middle one is the interesting one.

Almost a third of these deaths are recorded as "unknown cause". That is
not an evasion; it is an honest category for a death where the investigation
could not establish what happened. It also means the other two figures are
soft: a case that could have been ASSB with a more complete scene
investigation may end up in "unknown", which would move both numbers.

So the 28% for accidental suffocation is a floor rather than a measurement.

How the classification is made

Cause of death is assigned from the underlying cause ICD-10 codes on the
death certificate:

The figures come from the National Vital Statistics System mortality files,
with rates calculated through CDC WONDER.

Which means this breakdown is ultimately a record of what investigators and
certifiers wrote down — and the size of the "unknown" slice is the clearest
available measure of how often the circumstances of an infant's death cannot
be reconstructed.

*Source: CDC/NCHS, National Vital Statistics System, Mortality Files. Centers
for Disease Control and Prevention.*