How has the increase in preterm births affected the U.S. infant mortality rate?
In 2005, 68.6% of all infant deaths occurred to preterm infants, up from 65.6% in 2000. Very preterm infants accounted for only 2% of births, but over one-half of all infant deaths in both 2000 and 2005. Because the majority of infant deaths occur to very preterm infants, changes in either the percentage of these infants or in their infant mortality rate can have a large impact on the overall infant mortality rate. The infant mortality rate for very preterm infants was 183.24 infant deaths per 1,000 live births in 2005, not significantly different from the rate in 2000 (180.94), halting a long-term decline (1,2). The plateau in the U.S. infant mortality rate from 2000 to 2005 was largely due to the combination of the increase in the percentage of very preterm births and the lack of decline in the infant mortality rate for these births. However, the increase in the percentage of late preterm births has also had an impact.
