THE EPIDEMIC OF SIDS IN NORWAY 1967-93 - CHANGING EFFECTS OF RISK-FACTORS

Time trends on the association of maternal age, birth order, and marit al status with the risk of sudden infant death syndrome (SIDS) and non -SIDS deaths in Norway were analysed: 2356 postperinatal SIDS deaths a nd 4069 postperinatal non-SIDS deaths were ascertained during 1967-93. The SIDS incidence was 1.25 per 1000 in 1967, reached a peak of 2.69 in 1988, and fell to 1.22 in 1990 after the initiation of an intervent ion programme to avoid prone sleeping. In the entire period, young mat ernal age, high birth order, and unmarried motherhood were associated with SIDS. The adverse effects of young maternal age and high birth or der increased continuously with time. From 1967-71 to 1990-93, the rel ative risk for maternal age < 20 years v maternal age 25-29 changed fr om 2.5 (95% confidence interval 2.0 to 3.2) to 7.0 (95% CI4.2 to 11.9) (p < 0.0001), and for birth order 4+ v birth order I from 3.2 (95% CI 2.5 to 4.2) to 14.4 (95% CI 8.3 to 24.9) (p < 0.0001). Effects on non -SIDS deaths were far weaker and no secular trends were observed. The strong association of young maternal age, high birth order, and marita l status in SIDS, but not in non-SIDS, provides evidence that SIDS is an epidemiological entity. The increasing effects of young maternal ag e and high birth order, which continued after the sudden drop in the S IDS rate in 1990, suggest that further efforts to prevent SIDS should be aimed particularly at identifying causal mechanisms in high risk gr oups.