From 1940 to 2005 (most recent data available),infant, nenonatal, or postneonatal annual mortality rates in the United States declined considerably. The infant mortality rate decreased 85%,from 47 infant deaths per 1000 live births in 1940 to 6.87 in 2005. During the same period, substantial changes also occurred in the neonatal rate, and which decreased 84%,from 28.8 to 4.54 deaths per 1000 live births, and the postneonatal rate, and which decreased 87%,from 18.3 to 2.34 deaths per 1000 live births.
Source: cdc.gov