摘要：Objectives. We investigated the role of socioeconomic factors in Black–White disparities in preterm birth (PTB). Methods. We used the population-based California Maternal and Infant Health Assessment survey and birth certificate data on 10 400 US-born Black and White California residents who gave birth during 2003 to 2010 to examine rates and relative likelihoods of PTB among Black versus White women, with adjustment for multiple socioeconomic factors and covariables. Results. Greater socioeconomic advantage was generally associated with lower PTB rates among White but not Black women. There were no significant Black–White disparities within the most socioeconomically disadvantaged subgroups; Black–White disparities were seen only within more advantaged subgroups. Conclusions. Socioeconomic factors play an important but complex role in PTB disparities. The absence of Black–White disparities in PTB within certain socioeconomic subgroups, alongside substantial disparities within others, suggests that social factors moderate the disparity. Further research should explore social factors suggested by the literature—including life course socioeconomic experiences and racism-related stress, and the biological pathways through which they operate—as potential contributors to PTB among Black and White women with different levels of social advantage. Higher rates of preterm birth (PTB) among Blacks than Whites have been documented in the United States since at least the early 20th century. 1–3 This racial disparity is of great concern because PTB strongly predicts infant mortality 4,5 and adverse health and neurodevelopmental outcomes in childhood, 4,6,7 and has been linked with chronic disease, disability, and premature mortality in adulthood. 8–10 The underlying reasons for the racial disparity in PTB are not well understood. 4 A range of socioeconomic factors—including income, wealth, and education at the individual, household, and area levels—vary across racial/ethnic groups 11–16 and are biologically plausible underlying causes of PTB. 4,17–20 Socioeconomic effects on health, including PTB, could operate independently of and in concert with the effects of stressful experiences related more directly to racial discrimination. 4,16,21,22 Many studies have observed different PTB risks associated with socioeconomic or socioeconomically linked characteristics of the geographic areas where women reside, 4,11,23–32 including area-level measures of poverty, unemployment, 26 segregation, 24,28 and crime rates. 25 Various individual-, household-, and neighborhood-level socioeconomic factors could plausibly affect PTB through diverse causal pathways, including those involving poor nutrition or prepregnancy health status, adverse health-related behaviors, lack of medical care, social isolation, stress, and hazardous physical exposures in the home, neighborhood, workplace, or in transit. 4 Biological pathways leading from stressful experiences to PTB through neuroendocrine processes have been described. 33–36 A systematic review 17 of studies examining relationships between adverse birth outcomes and socioeconomic factors found that 93 of 106 studies reported a significant association, overall or within a subgroup, between a socioeconomic measure and a birth outcome; effects varied, however, across racial/ethnic groups and socioeconomic measures. Several birth outcome studies have examined interactions between variables reflecting racial/ethnic group and socioeconomic factors, with inconsistent results. Some studies have found minimal or no Black–White differences in PTB among highly disadvantaged women. 37–39 Others have observed a significant racial disparity among socioeconomically disadvantaged women, but an even greater disparity among more socioeconomically advantaged women. 24,40,41 Some other studies, however, have not reported differences in the racial disparity in PTB across socioeconomic subgroups. 4 Although the biological mechanisms for low birth weight are thought to be distinct from those for PTB, 4 several studies 42–49 have observed relatively smaller—but not necessarily small—racial disparities in low birth weight or infant mortality within socioeconomically disadvantaged versus more advantaged subgroups. In some studies, the Black–White disparity in PTB has persisted after adjustment for socioeconomic and other known or suspected risk factors, 31,50–52 leading some researchers to conclude that the Black–White disparity in PTB reflects underlying genetic differences. 53–56 Others have challenged this, noting that the disparity may reflect significant unmeasured socioeconomic factors and other social experiences including those related to racial discrimination throughout life, not only during pregnancy. 18,21,57–62 With few exceptions, 30,31,39,63,64 however, most studies of the Black–White disparity in PTB have had limited socioeconomic information, and few have examined systematically how the disparity may vary at different socioeconomic levels. The goal of this study was to investigate the role of socioeconomic factors in the Black–White disparity in PTB by using a unique population-based data source on California births with more extensive information than generally available in previous PTB research, including multiple socioeconomic measures at the individual, household, and area levels and a wide range of covariables reflecting potential confounders suggested by the literature. The aim was to assess the combined contribution of multiple socioeconomic factors—representing different dimensions of social advantage and disadvantage—to the racial disparity in PTB, and to examine whether and how these socioeconomic factors might moderate the relationship between racial group and PTB.
