240: Explaining the recent decrease in US infant mortality rate, 2007-2013

Abstract

ObjectiveBetween 2007 and 2013 the US infant mortality rate declined steadily, along with a decline in the preterm birth rate, from 6.75 to 5.96 deaths per 1000 live births. The aim of this study was to explain the decrease in infant mortality by decomposing the rate difference between 2013 and 2007 into the proportion due to change in the distribution of gestational age and the proportion due to change in gestational age-specific mortality.Study DesignThe US period linked birth-infant death files were used to enumerate births and infant deaths for 2007 and 2013 at each week of gestational age. The proportion of births at each gestational week and the gestational age-specific mortality for each week were calculated. Births and deaths were excluded if gestational age was missing. The Kitagawa decomposition method was used to partition the changes at each gestational week and the overall reduction in infant mortality into the fractions due to change in the distribution of gestational age at birth and to change in the gestational age-specific mortality.ResultsInfant mortality rates were 6.62 and 5.90 for 2007 and 2013 respectively (-0.72 per 1000 livebirths). In general, the proportion of births at preterm gestational ages and the gestational-age specific mortality rates at each gestational age decreased between 2007 and 2013. Decomposing the overall decrease in infant mortality resulted in apportioning 36 percent of the decline to changes in the distribution of gestational age and 64 percent to decreases in gestational age-specific mortality (Table). Patterns were not explained by births and deaths missing gestational age data.Conclusion ObjectiveBetween 2007 and 2013 the US infant mortality rate declined steadily, along with a decline in the preterm birth rate, from 6.75 to 5.96 deaths per 1000 live births. The aim of this study was to explain the decrease in infant mortality by decomposing the rate difference between 2013 and 2007 into the proportion due to change in the distribution of gestational age and the proportion due to change in gestational age-specific mortality. Between 2007 and 2013 the US infant mortality rate declined steadily, along with a decline in the preterm birth rate, from 6.75 to 5.96 deaths per 1000 live births. The aim of this study was to explain the decrease in infant mortality by decomposing the rate difference between 2013 and 2007 into the proportion due to change in the distribution of gestational age and the proportion due to change in gestational age-specific mortality. Study DesignThe US period linked birth-infant death files were used to enumerate births and infant deaths for 2007 and 2013 at each week of gestational age. The proportion of births at each gestational week and the gestational age-specific mortality for each week were calculated. Births and deaths were excluded if gestational age was missing. The Kitagawa decomposition method was used to partition the changes at each gestational week and the overall reduction in infant mortality into the fractions due to change in the distribution of gestational age at birth and to change in the gestational age-specific mortality. The US period linked birth-infant death files were used to enumerate births and infant deaths for 2007 and 2013 at each week of gestational age. The proportion of births at each gestational week and the gestational age-specific mortality for each week were calculated. Births and deaths were excluded if gestational age was missing. The Kitagawa decomposition method was used to partition the changes at each gestational week and the overall reduction in infant mortality into the fractions due to change in the distribution of gestational age at birth and to change in the gestational age-specific mortality. ResultsInfant mortality rates were 6.62 and 5.90 for 2007 and 2013 respectively (-0.72 per 1000 livebirths). In general, the proportion of births at preterm gestational ages and the gestational-age specific mortality rates at each gestational age decreased between 2007 and 2013. Decomposing the overall decrease in infant mortality resulted in apportioning 36 percent of the decline to changes in the distribution of gestational age and 64 percent to decreases in gestational age-specific mortality (Table). Patterns were not explained by births and deaths missing gestational age data. Infant mortality rates were 6.62 and 5.90 for 2007 and 2013 respectively (-0.72 per 1000 livebirths). In general, the proportion of births at preterm gestational ages and the gestational-age specific mortality rates at each gestational age decreased between 2007 and 2013. Decomposing the overall decrease in infant mortality resulted in apportioning 36 percent of the decline to changes in the distribution of gestational age and 64 percent to decreases in gestational age-specific mortality (Table). Patterns were not explained by births and deaths missing gestational age data. Conclusion