Racial residential segregation and low birth weight in Michigan's metropolitan areas

Objectives. We examined the influence of racial residential segregation, independent of neighborhood economic factors, on the overall and specific etiological risks of low birth weight.Methods. We geocoded all singleton births in Michigan metropolitan areas during 2000 to census tracts. We used hierarchical generalized linear models to investigate the association between low birth weight (< 2500 g) and neighborhood-level economic and racial segregation, controlling for individual and neighborhood characteristics. We analyzed competing risks of the 2 etiologies of low birth weight: intrauterine growth restriction and preterm birth.Results. Living in a Black segregated area was associated with increased odds (odds ratio [OR] = 1.15; 95% confidence interval [CI] = 1.03, 1.29; P < .05) of low birth weight after adjusting for individual- and tract-level measures. The analysis suggested that the association between low birth weight and racial segregation was attributable primarily to increased risk of intrauterine growth restriction (OR = 1.19; 95% CI = 1.03, 1.37; P < .05).Conclusions. Odds of low birth weight are higher in racially segregated Black neighborhoods in Michigan''s metropolitan areas, independent of economic factors. The association appears to operate through intrauterine growth restriction rather than preterm birth.As the leading cause of death among non-Hispanic Black infants and second-leading cause of death among non-Hispanic White infants, complications related to short gestation and low birth weight represent a significant clinical and public health issue.^1–3 Low birth weight also leads to long-term health consequences through increased rates of childhood and adult chronic diseases.^3–6 Racial disparities in rates of low birth weight have persisted even as total infant mortality has declined and prenatal care utilization among women of color has increased.^1–3 Because differences in individual-level risk factors cannot completely explain the differences in outcomes for White and Black mothers,^3,7 researchers have begun investigating contextual influences on racial disparities in birth outcomes.^3,8Racial segregation is a contextual factor that might contribute to racial disparities in low birth weight by isolating Blacks from the resources and opportunities found more frequently in White communities.^9–13 Residents in Black segregated neighborhoods accumulate less home equity,^14,15 have decreased access to quality primary education,¹⁶ and are exposed to greater residential and economic instability than are residents of nonsegregated communities.⁹ The accumulation of disadvantages in racially isolated neighborhoods could lead to negative birth outcomes for women by limiting opportunities associated with improved health (e.g., educational opportunities or access to quality medical care) and by exposing them to increased stress from neighborhood-level factors.Evidence from a small number of studies suggests that low birth weight is associated with racial residential segregation.^17–24 With few exceptions,^17,25,26 studies link metropolitan-level segregation or the percentage of Black residents in a community to low birth weight. However, because isolation is inherently spatial, to understand how the racial isolation of an individual mother''s neighborhood affects her pregnancy outcomes, isolation is most appropriately measured by considering her neighborhood along with its immediate surroundings (e.g., bordering neighborhoods) rather than by the metropolitan area or a single neighborhood.¹⁷Some authors have argued that racial segregation simply serves as a proxy for economic segregation.^27,28 By contrast, we posit that racial segregation is a distinct form of neighborhood-level disadvantage that presents an increased risk for low birth weight beyond that caused by economic segregation. Sociologists have shown that, even in the presence of economic segregation, the circumstances of racially segregated Black neighborhoods differ from those of White neighborhoods at similar socioeconomic levels.^29–32 This means that although residents of Black middle-class neighborhoods may live in residential areas that are separate from poor Black neighborhoods, they have greater exposure than do middle-class Whites to negative contextual factors and have fewer resources in their vicinity. This also suggests that any attempt to distinguish between the effects of racial and economic segregation on low birth weight requires that economic segregation also be measured spatially, taking a mother''s neighborhood and its immediate surroundings into account.It is also important to consider that the drivers of low birth weight—preterm birth and intrauterine growth restriction—have distinct physiological mechanisms.^33–35 Assessing the degree to which racial isolation is associated with each can provide important insight into the etiological mechanisms relating racial segregation to low birth weight. Spontaneous preterm birth is commonly precipitated by an infection,^36–40 which could be associated with racial segregation if, for instance, racial segregation reduces access to quality care.²⁵ Intrauterine growth restriction, on the other hand, typically stems from a chronic deficiency in oxygen and nutrient delivery to the fetus.^41–46 Chronic stress associated with the circumstances of racially isolated neighborhoods might affect placental vasculature function, creating an oxygen–nutrient insufficiency that leads to intrauterine growth restriction.⁴⁷ We know of no research that has considered the competing risks of growth restriction and preterm birth in the relationship of neighborhood environments with low birth weight.We examined births to mothers living in Michigan metropolitan areas to ascertain whether neighborhood racial segregation was associated with low birth weight independent of economic factors. We explicitly captured the spatial nature of both racial and economic segregation through a localized segregation index. We also analyzed the degree to which racial segregation was associated with different etiologies of low birth weight.