The relationship between low birth weight and socioeconomic status in Ireland.

There is now fairly substantial evidence of a socioeconomic gradient in low birth weight for developed countries. The standard summary statistic for this gradient is the concentration index. Using data from the recently published Growing Up in Ireland survey, this paper calculates this index for low birth weight arising from preterm and intrauterine growth retardation. It also carries out a decomposition of this index for the different sources of low birth weight and finds that income inequality appears to be less important for the case of preterm births, while father's education and local environmental conditions appear to be more relevant for intrauterine growth retardation. The application of the standard Blinder-Oaxaca decomposition also indicates that the socioeconomic gradient for low birth weight appears to arise owing to different characteristics between rich and poor, and not because the impact of any given characteristic on low birth weight differs between rich and poor.