Prematurity and race account for much of the interstate variation in infant mortality rates in the United States.

OBJECTIVE

To assess the correlation between infant mortality and extreme prematurity by state.

STUDY

DESIGN

This ecological study included data on 28,526,534 infants from 2007 to 2013 in all 50 US states and DC using CDC WONDER linked birth and infant death records. Regression analyses determined the correlation between infant and neonatal mortality rates and the proportion of extremely preterm, extremely low birth weight, and black births by state.

RESULTS

State infant and neonatal mortality rates were directly and highly correlated with the proportion of extremely preterm births (infant, r2 = 0.71, P < 0.001; neonatal, r2 = 0.77, P < 0.001) and extremely low birth weight births (r2 = 0.63, P < 0.001; r2 = 0.73, P < 0.001). The proportion of black births also correlated directly with infant and neonatal mortality rates.

CONCLUSIONS

Interstate variation in infant and neonatal mortality rates are primarily driven by rates of extremely preterm and extremely low birth weight births which is closely related to the proportion of black births.