Sudden infant death syndrome and post perinatal mortality in Norwegian birth cohorts 1967-1980.

The well established effects of maternal age and birth order in sudden infant death syndrome (SIDS) formed the basis for a comparison with other categories of post perinatal death in an attempt to shed some light on the etiologic roles played by ante and postnatal factors. A total of 826,162 children, born 1967 through 1980 and recorded at the Medical Birth Registry of Norway was at risk to die during the post perinatal period (ages 7 through 364 days). Out of the 3,582 infants who died, 1,062 were considered SIDS. Strong effects of maternal age (negative) and birth order (positive) were found in the SIDS group, but not to the same extent in the non-SIDS group or the group of congenital malformations. Likewise, the excess risk in children of unmarried mothers was higher in the SIDS group. The suggested effects of postnatal factors in the causation of SIDS may seem promising from a preventive point of view. The strength of the effects of maternal age and birth order necessitate adjustment for these variables in future epidemiological studies of SIDS.