摘要：Objectives. To compare associations between socioeconomic status and low birth weight across the United States, the United Kingdom, Canada, and Australia, countries that share cultural features but differ in terms of public support and health care systems. Methods. Using nationally representative data from the United States (n = 8400), the United Kingdom (n = 12 018), Canada (n = 5350), and Australia (n = 3452) from the early 2000s, we calculated weighted prevalence rates and adjusted odds of low birth weight by income quintile and maternal education. Results. Socioeconomic gradients in low birth weight were apparent in all 4 countries, but the magnitudes and patterns differed across countries. A clear graded association between income quintile and low birth weight was apparent in the United States. The relevant distinction in the United Kingdom appeared to be between low, middle, and high incomes, and the distinction in Canada and Australia appeared to be between mothers in the lowest income quintile and higher-income mothers. Conclusions. Socioeconomic inequalities in low birth weight were larger in the United States than the other countries, suggesting that the more generous social safety nets and health care systems in the United Kingdom, Canada, and Australia played buffering roles. Socioeconomic inequalities in health are pervasive in the developed world, a fact that has led to questions about the extent of health inequalities across countries. Yet, despite a developing literature on health across Organisation for Economic Co-operation and Development countries, relatively little is known about inequalities in health across countries or at what point during the life course socioeconomic inequalities in heath emerge. A few studies have compared income gradients in parent-reported child health status in the United States with those in the United Kingdom, Canada, or Australia, but the purpose of those studies was not to document cross-country comparisons. 1–5 Other studies incorporating objective health measures have shown that socioeconomic gradients in health are very similar in the United States and United Kingdom throughout the life course, despite better overall population health in the United Kingdom; however, health measures for young children were limited in those studies. 6,7 As such, little is known about how socioeconomic gradients in health at very young ages compare across countries. Low birth weight (LBW) is an important measure of health at the “starting gate” because it is a leading risk factor for infant mortality as well as a marker for subsequent child morbidity among infants who survive 8 ; it is also an important predictor of health and socioeconomic status over the life course and across generations. 9 In the United States, there is clear evidence of a socioeconomic gradient in LBW, although patterns vary by race/ethnicity. 10,11 Little is known about the magnitude of socioeconomic gradients in health at birth in other developed countries. We used nationally representative data from 4 countries—the United States, the United Kingdom, Canada, and Australia—to compare socioeconomic gradients in LBW across English-speaking countries that share cultural features but differ in terms of public support and health care systems. The United Kingdom, Canada, and Australia enjoy better overall population health than the United States 12 and also have more generous health care and social support systems. 12,13 All 4 countries are diverse, with relatively large immigrant populations but different racial/ethnic mixes. 14 Canada and Australia have lower income inequality than the United States and United Kingdom, as measured by Gini coefficients, 13 and there is increasing evidence that income inequality adversely affects population health. 15 For most of these reasons, we expected that socioeconomic gradients in LBW would be largest in the United States.
