Artful Dodger:

"Although previous reports have documented that rates of low birthweight and intrauterine growth retardation are higher among infants of women living in poverty, the infant mortality risk among infants born to women with low incomes has not been characterized recently. To analyze the relation between parental low income and infant mortality, CDC analyzed data from the 1988 National Maternal and Infant Health Survey (NMIHS) (the most recent data available). This report presents the findings of the analysis and indicates that for women with household incomes below the poverty level * in 1988, the infant mortality rate was 60% higher and the postneonatal mortality rate was twice as high as those for women living above poverty level."

"An infant death was defined as the death of a live-born infant before his or her first birthday; a neonatal death, as the death of a live-born infant less than 28 days after birth; and a postneonatal death, as the death of a live-born infant 28-364 days after birth."

http://www.cdc.gov/mmwr/preview/mmwrhtml/00039818.htm