Ethnic Density Effects on Birth Outcomes and Maternal Smoking During Pregnancy in the US Linked Birth and Infant Death Data Set

Objectives. We investigated whether mothers from ethnic minority groups have better pregnancy outcomes when they live in counties with higher densities of people from the same ethnic group—despite such areas tending to be more socioeconomically deprived.Methods. In a population-based US study, we used multilevel logistic regression analysis to test whether same-ethnic density was associated with maternal smoking in pregnancy, low birthweight, preterm delivery, and infant mortality among 581 151 Black and 763 201 Hispanic mothers and their infants, with adjustment for maternal and area-level characteristics.Results. Higher levels of same-ethnic density were associated with reduced odds of infant mortality among Hispanic mothers, and reduced odds of smoking during pregnancy for US-born Hispanic and Black mothers. For Black mothers, moderate levels of same-ethnic density were associated with increased risk of low birthweight and preterm delivery; high levels of same ethnic density had no additional effect.Conclusions. Our results suggest that for Hispanic mothers, in contrast to Black mothers, the advantages of shared culture, social networks, and social capital protect maternal and infant health.Numerous studies have shown that living in a socioeconomically deprived neighborhood exerts a contextual effect on the health of individual residents beyond their own socioeconomic status.^1,2 This is likely to have a differential impact on some ethnic minority groups, such as African Americans and Hispanics. (Throughout this paper we have defined “ethnicity” as a global indicator of a person''s heritage including both racial and ethnic origins.) Whereas the majority of poor White people live in nondeprived areas, poor African Americans are concentrated in areas of high poverty.³ Thus, it might be paradoxical to suggest that members of ethnic minority groups might be healthier when they live in areas with a high concentration of people of the same ethnicity.^4,5 However, there is some evidence that living in communities that contain proportionally more people from the same ethnic group is protective for some health outcomes, once material deprivation is accounted for. The evidence for the protective effects of same-ethnic density is strongest for mental health,^4,5 with the evidence for maternal and infant health outcomes more mixed.The majority of studies that have investigated the impact of same-ethnic density on maternal and infant health have focused on African Americans or Black families (in this article, we use whichever term was used in the studies we describe). Two older ecological studies^6,7 found that increasing levels of same-ethnic density for New York City African Americans were associated with increased fetal and neonatal mortality but not postneonatal mortality. Another study found no association between ethnic density measured in US cities and postneonatal mortality.⁸ More recent studies have tended to use multilevel analyses that controlled for individual-level measures of socioeconomic status, and focused on measures of morbidity, such as low birthweight (LBW), with less consistent results.^9–14One study of Chicago neighborhoods found that an increasing proportion of African American residents was associated with a reduced risk of LBW.¹³ Two other studies found that an increasing proportion of Black residents was associated with increased risk of LBW.^11,14 However, other studies have found no significant associations between same-ethnic density and LBW.^9,10,12Five studies have investigated the impact of ethnic density on preterm delivery rates among African Americans.^{9,10,12,15,16} Studies of neighborhoods in Minnesota⁹ and North Carolina¹⁵ found same-ethnic density to be associated with increased risk of preterm delivery after adjustment for individual but not area measures of socioeconomic circumstances. Three other studies found no association between same-ethnic density and preterm delivery in models that included individual-level maternal education and area-level measures of socioeconomic circumstances.^10,12,16We are aware of only 1 study that has investigated the impact of same-ethnic density on maternal smoking during pregnancy, which found that it was associated with reduced risk of maternal smoking after adjustment for both individual and area measures of socioeconomic conditions.¹⁷We found only 2 studies that have investigated the impact of ethnic density on Hispanic maternal and infant health. The first, conducted in the states of Arizona, California, New Mexico, and Texas, found lower rates of infant mortality for US-born Mexican-origin mothers living in counties with high concentrations of mothers of the same ethnicity.¹⁸ However, this effect was not found for mothers born outside the United States. The second study found no associations between same-ethnic density, as measured in Chicago census tracts, and LBW, preterm delivery, and maternal smoking after adjustment for economic disadvantage, maternal education, and violent crime.¹²Further support for the protective effects of Hispanic density comes from the “Hispanic paradox.”¹⁹ Compared with the White majority population, Hispanic mothers tend to have better or equal pregnancy outcomes and better health-related behaviors despite generally having more disadvantaged socioeconomic circumstances.^20–24 It has been proposed that this “paradox” can be explained by dietary factors, social support and cohesion, and cultural differences in relation to the importance of motherhood.^23,24 However, long-term US residents who move away from ethnic enclaves²⁵ are more likely to adopt Western health behaviors and values²⁶ and may lose any protective effects of Hispanic culture. Thus, the protective effects of Hispanic culture are more likely to be maintained in communities of higher Hispanic density.We hypothesized that maternal smoking during pregnancy, infant mortality, LBW, and preterm birth would be lower for non-Hispanic Black and Hispanic White (hereafter referred to as “Hispanic mothers”) mothers living in counties with a higher percentage of people of the same ethnicity, relative to their counterparts living in counties with a low percentage of people of the same ethnicity.