interact such that individual-level characteristics may exert a greater influence in certain neighborhoods or such that the effects of the neighborhood context are more pronounced for subgroups of women stratified by socioeconomic condition, race-ethnicity, or other individual attributes. For example, a recent study in Chicago found that high perceived levels of neighborhood support were positively associated with birth weight only for white infants. A significant negative association between birth weight and neighborhood-level economic disadvantage was documented for African American infants (Buka et al., 2003). This association remained significant even after adjustment for maternal characteristics and other neighborhood conditions (Casey and McDonald, 1988). O’Campo and colleagues (1997) found that the early initiation of prenatal care did not have the same beneficial effect for women living in disadvantaged neighborhoods in Baltimore, raising the possibility that prenatal care in deprived settings is unable to address various risks associated with adverse birth outcomes (Holzman et al., 1998; Kaufman et al., 1997). Evidence also suggests that prenatal care has no effect on preterm birth (see Chapter 9 for a discussion).

Effect modification in multilevel models also occurs. This type of effect modification is perhaps most difficult to conceptualize and test because it implies a kind of cross-level effect by which individual-level effects are moderated by community-level conditions. This would mean, for example, that the effect of cigarette smoking on an individual’s risk of preterm birth would depend on some attribute of the community in which that individual resides. This effect modification would not be explained by interactions with other individual-level psychological or social exposures. In a study of community characteristics and child maltreatment, The Project on Human Development in Chicago Neighborhoods found that neighborhood social networks interacted with Hispanic ethnicity to affect the amount of physical abuse committed by individual families (Molnar et al., 2003). The authors interpreted this finding to make the point that neighborhood-level interventions may be the most effective way to reduce rates of the child abuse in certain populations. Such findings suggest that studies that examine factors at only one level (either the individual level only or the ecological level only) may underestimate the effects of the social environment and potentially miss an opportunity to use interventions to the reduce risk associated with any particular factor.

Exposure to acute and chronic stress is one of the hypothesized pathways through which neighborhood context may affect birth outcomes. At the individual level, a growing body of empirical evidence, based on methodologically rigorous studies of pregnant women of different racial-ethnic,