Age at death and risk factors in sudden infant death syndrome.

The age at death curve of the Sudden Infant Death Syndrome (SIDS) is considered to be its most unique characteristic. Investigation of SIDS in Cook County, Illinois, for the years 1975-80 indicate that: it is similar to that observed for SIDS in numerous other geographical areas, with low neonatal rates, high rates during the first 2-3 months of life and declining rates thereafter; the age at death for SIDS significantly differs from that of 21 other causes of infant mortality; and the age at death is independent of risk factors such as race, birthweight, urbanization, the month in which prenatal care was initiated, maternal age, legitimacy, gender and seasonality, all of which factors are quantitatively associated with SIDS mortality rates. These observations indicate that the aetiology of SIDS may be multifactorial with the underlying mechanism, which may be associated with normal growth and development, operating primarily in the period of high susceptibility i.e. at 2-4 months of age. Secondary factors, possibly present since birth, operate during this period of high susceptibility. Any suggested underlying aetiology for SIDS must account for the unique age at death pattern.