Primary care, infant mortality, and low birth weight in the states of the USA

Study objective: The study tests the extent to which primary care physician supply (office based primary care physicians per 10 000 population) moderates the association between social inequalities and infant mortality and low birth weight throughout the 50 states of the USA. Design: Pooled cross sectional, time series analysis of secondary data. Analyses controlled for state level education, unemployment, racial/ethnic composition, income inequality, and urban/rural differences. Contemporaneous and time lagged covariates were modelled. Setting: Eleven years (1985-95) of data from 50 US states (final n = 549 because of one missing data point). Main results: Primary care was negatively associated with infant mortality and low birth weight in all multivariate models (p<0.0001). The association was consistent in contemporaneous and time lagged models. Although income inequality was positively associated with low birth weight and infant mortality (p<0.0001), the association with infant mortality disappeared with the addition of sociodemographic covariates. Conclusions: In US states, an increased supply of primary care practitioners - especially in areas with high levels of social disparities - is negatively associated with infant mortality and low birth weight.