Use of new Nordic criteria for classification of SIDS to re-evaluate diagnoses of sudden unexpected infant death in the Nordic countries.

To investigate whether changes in diagnostic practice might be the cause of the SIDS epidemic in the Nordic countries in the 1970s and 1980s a cooperative study was initiated in 1990. Common morphologic diagnostic criteria for SIDS were established in 1992 and 127 randomly selected sudden unexpected infant deaths from all Nordic countries from 1970 to 1995 and 205 cases from the Institute of Forensic Medicine, Oslo, Norway (RMI) from 1984 to 1995 were re-evaluated blindly using the new criteria. Neither the increase nor the decline in the SIDS rate since 1989 seemed to be due to changed diagnostic practices. SIDS seemed to have been under-diagnosed before the new criteria came into operation in 1992. There were fewer discrepancies between the original and revised diagnoses in the RMI cases than in the rest of the Norwegian cases, both before and after 1992.