Socioeconomic Disparities in Infant Health: An International Comparison

Purpose: Socioeconomic (SES) inequality in health is a pervasive international social welfare issue. In the United States (US), there is evidence of a clear SES gradient in infant low birthweight, though the gradient varies by race/ethnicity. Low birthweight is an important marker for future child health and wellbeing and offers an opportunity for early intervention—both at the micro and macro-policy level. The literature on children’s gradients in health in other countries is inconclusive about whether health patterns by income are similar to or different from those found in the US, and no study has conducted cross-national comparisons of SES gradients in birth outcomes. This paper uses data from three highly comparable, nationally representative child cohort studies to compare SES gradients in birth outcomes in Australia, the United Kingdom (UK), and the US. Two contrasting theoretical frameworks are examined: 1) If neo-materialist theoretical explanations (eg. disadvantaged life conditions) are driving SES gradients in child health, the SES gradient should be larger in the US than in Australia or the UK  due to higher poverty rates and weaker social and health safety net. 2) If relative social position or social comparison is driving health inequality, then similar gradients in these countries are expected, as societal inequality is pervasive in all three nations.

Method: This paper using the three national datasets: The Longitudinal Study of Australian Children – Birth Cohort (LSAC), the Millennium Cohort Study for the UK (MCS), and the Early Childhood Longitudinal Study – Birth Cohort and Fragile Families studies for the US (ECSL-B). The outcomes of interest include birthweight, low birthweight, and small for gestational age. The independent variables of interest are weighted income quintiles. A rich set of covariates are included in the models. The svy procedures in Stata SE 12 are used to adjust for sampling design in the calculation of weighted rates of low birthweight and logistic regression models (Odds Ratios).

Results: The results demonstrate clear SES gradients in low birthweight among infants in all three countries, where lower income is associated with higher rates of low birthweight births. The logistic regression models demonstrate that low and middle income women are significantly more likely to have a low birthweight infant in all three countries. However, in the fully adjusted logistic regression model, the graded relationship between income and low birthweight becomes attenuated. We find that the association between low income and low birthweight status is strongest in the US (OR=1.7) and Australia (OR=1.8), and lowest in the UK (OR=1.4). Associations in all three countries are statistically significant at p<.05.

Conclusion and Implications: Income inequality in low birthweight is as pervasive in Australia and the UK as it is in the US. Despite different social welfare and health care systems in Australia and the UK, infants born in these countries also experience health inequalities by income. This finding suggests support for societal inequality and relative social position as important factors driving SES inequalities in birth outcomes internationally, and social welfare policies that reduce inequality may benefit infant health.