Socioeconomic status and risk of infant death. A population-based study of trends in Norway, 1967-1998

BACKGROUND: The aim of this study was to examine the association between socioeconomic status and risk of infant death in Norway from 1967 to 1998. METHODS: Information from the Medical Birth Registry of Norway on all live births and infant deaths was linked to information from Statistics Norway on parents' education. There were 1777364 eligible live births and 15517 infant deaths. Differences between education groups were estimated as risk differences, relative risks, population attributable fractions, and index of inequality ratios. RESULTS: The risk of infant death decreased in all education groups, and the level of education increased over time. The trends differed for neonatal and postneonatal death. For neonatal death the risk difference between infants whose mothers had high and low education was reduced from 3.5/1000 in the 1970s to 0.9/1000 in the 1990s. The relative index of inequality (RII) for maternal education decreased from 1.72 to1.32. The proportion of neonatal deaths that could be attributed to <13 years of education decreased from 22.3 to 8.4. For postneonatal death the risk difference between infants whose mothers had high and low education increased from 0.7/1000 in the 1970s to 2.0/1000 in the 1990s. The RII for maternal education increased from 1.31 to 4.00. The population attributable fraction increased from 9.7 to 39.5. CONCLUSIONS: An inverse association between socioeconomic status and risk of postneonatal death persists, albeit there was a considerable reduction in risk between 1967 and 1998.