The objective of this study was to quantify the effect of socioeconomic status (SES) on health outcomes during the first year after newborn discharge among infants with complex chronic conditions (CCCs) insured through a universal health plan. The design used was longitudinal, population-based cohort study in Ontario, Canada.

Infants born in hospitals from April 1, 1996, through March 31, 2000. Infants with CCCs were identified from their newborn discharge records. Neighborhood income quintiles were obtained by linking participants' postal codes to census data. 

Mortality and hospital admissions in the first year after newborn discharge. Logistic and Poisson regression analyses were used to examine the relationship between neighborhood income quintiles and outcomes, adjusting for important covariates such as low birth weight and rural residence.

A total of 512,768 infants were included, of whom 2.3% had CCCs at newborn discharge. Infants with CCCs accounted for 37.8% of deaths and 11.0% of hospitalizations during the first year after the newborn discharge. Infants with CCCs living in the lowest-income neighborhoods had a 1.26-fold higher mortality risk (95% confidence interval, 0.83-1.90; P = .28) and a 1.24-fold higher hospitalization rate (1.09-1.40; P < .001) compared with those living in the highest-income neighborhoods. Although the income gradients associated with mortality and hospitalization were less pronounced among infants with CCCs compared with infants without CCCs, the absolute interquintile risk differences attributable to SES were higher among infants with CCCs.

Despite universal health insurance, SES-related inequality affects hospitalization and, possibly, mortality rates among medically vulnerable infants.