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Over the past decade, two risk factors have emerged as promising explanations for the racial disparities in preterm birth rates: stress and infection. As reviewed in Chapter 3, a growing body of research suggests that maternal psychological stress is associated with an increased risk for preterm delivery. Insofar as African American women may experience more stress in their daily lives than white women, it has been suggested that maternal stress may contribute to the disparities in preterm birth rates between African American and white women (James, 1993). For example, Lu and Chen (2004) reported that African American women were significantly more likely to experience stressful life events (e.g., to lose a job or to become separated or divorced) just before or during pregnancy than non-Hispanic white women. As discussed in Chapter 3, African American women are also more likely to experience racism, which can be conceptualized as an additional source of stress (Krieger, 2000).

African American women are more likely than white women to experience a number of infections, including bacterial vaginosis and sexually transmitted infections (Fiscella, 1995; Meis et al., 2000). Insofar as these infections are associated with preterm delivery, they may be responsible for a significant portion of the racial disparities in preterm birth rates (Fiscella, 1995). However, the cause of this increased susceptibility to infections among pregnant African American women remains largely unknown, and to date antibiotic treatment of infections (other than for asymptomatic bacteriuria) during pregnancy has yielded modest or no benefits (Carey et al., 2000; McDonald et al., 2005) (see Chapter 9).

Genetic differences have often been invoked to account for racial disparities in a number of birth outcomes, including preterm birth. Although a woman’s genetic makeup undoubtedly plays a role in the pathogenesis of preterm birth, the potential genetic contribution to racial disparities in preterm birth is unknown. First, it is not known which genes contribute to racial disparities in preterm birth rates. For example, interleukin-6 (IL-6), gamma interferon (IFN-γ), and tumor necrosis factor alpha (TNF-α) have all been implicated in the pathogenesis of preterm birth. Although several population-based studies have shown that African Americans are more likely than whites to carry genotypes that induce a high level of expression of IL-6 (Cox et al., 2001; Hassan et al., 2003; Hoffmann et al., 2002), the findings for IFN-γ and TNF-α are less consistent; in some studies the prevalence of individuals with genotypes that induce high levels of expression of these two proinflammatory cytokines was actually lower among African Americans than whites (Cox et al., 2001; Hassan et al., 2003; Hoffman et al., 2002). Second, it is not known how genes interact with the environment to produce racial disparities in preterm birth. Geneticists recognize that the causes of most common,complex diseases and conditions, including preterm birth, consist of a complicated interaction between genes and the environ-



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