摘要：Objectives . This study assessed the contribution of age and other risk factors to racial disparities in rates of moderately low birthweight (MLBW; 1500–2499 g) and very low birthweight (VLBW; <1500 g). Methods . Logistic regression models were developed to determine the effects on MLBW and VLBW of maternal age, race, and poverty, adjusting for birth order, smoking, substance abuse, marital status, and educational level. The sample consisted of 158 174 singleton births to US-born African American and White women in New York City between 1987 and 1993. Results . The effects of maternal age on MLBW varied by race and poverty, with the most extreme effects among poor African American women. The effects of maternal age on VLBW also varied by race, but these effects were not moderated by poverty. Community poverty had a significant effect on MLBW among African American women, but no effect on VLBW. The adverse effect of older maternal age on MLBW and VLBW did not vary with community poverty. Conclusions . Older maternal age is associated with reduced birthweight among infants born to African American women, and the age effect is exacerbated by individual poverty. The persistence of a Black–White gap in low birthweight (LBW) and very low birthweight (VLBW) rates in the United States continues to be a serious public health problem. African American infants are more than twice as likely as White infants to be born weighing less than 2500 g (14.2% vs 6.3%), and almost 3 times as likely to be born weighing less than 1500 g (3.1% vs 1.2%). 1 The vast majority of births under 1500 g are associated with preterm delivery—the leading cause of death among African American infants in the United States. 2, 3 For the most part, the risks for LBW and VLBW births have been “individualized,” emphasizing those characteristics of individuals that increase the likelihood of a low-weight delivery rather than environmental and social factors affecting population rates. 4 Although African American women carry a disproportionate burden of individual risk factors, such as unmarried status and late entry into prenatal care, 5 racial differences in the distribution of such risks do not explain the disparity in birth outcomes, 6 nor are interventions based on these factors likely to reduce the racial gap. 7– 9 Furthermore, some individual risk factors operate differently across racial/ethnic groups, 10– 15 making it difficult to adjust meaningfully for confounders in studies involving multiple racial groups and potentially biasing estimates of effect. 16 Recent reports suggest that older maternal age is also associated with increased risk of low birthweight among singletons, but this effect has been described among African American women only. 17– 19 Geronimus has termed the deterioration in reproductive health status over the childbearing years among African American women “weathering.” 11 Although these findings suggest that maternal age operates differently for African American and White women, studies of birth outcomes generally treat this factor as a covariate or confounder, rather than exploring the joint impact of maternal age, race, and other risk factors. Recently, there has been renewed public health interest in the role of community and other social-structural factors as determinants of birth outcomes, 20– 23 providing additional insight into racial disparities. For example, rates of LBW and VLBW are higher in US cities than the suburbs or the nation as a whole, 24 with the highest rates found in the largest cities. 25 Ecological influences on birth outcomes have also been demonstrated within racial/ethnic groups, further supporting the idea that residential context (or factors associated with residential context) may have important health consequences. Polednak found that infant mortality rates among African Americans differed by degree of racial segregation, possibly because highly segregated areas are characterized by extremely concentrated poverty, inadequate health care, substandard housing, crime, and other stressors. 26 Consistent with this finding is a report that rates of LBW (specifically, intrauterine growth retardation) among lowincome African Americans are higher for women who reside in more violent, as compared with less violent, communities. 27 Finally, a number of studies have shown that African American women born in the United States have higher rates of LBW than African American women born outside the United States, suggesting the importance of nativity in addition to community of current residence. 28, 29 The question arises as to whether maternal age operates as a risk factor for pregnant women entirely at the individual level (possibly in concert with other individual-level risk factors) or whether the aging effect also expresses the cumulative impact of some higher-level conditions or exposures on birth outcomes. 8 At first look, maternal age would seem to offer little explanation for the Black–White gap in LBW or VLBW rates. To begin with, a racial gap is clearly evident at all maternal ages. 5– 7 In addition, the distribution of births by maternal age peaks much earlier for African Americans than for Whites, so that a larger proportion of African American births occur to women who are actually at lowest risk for LBW delivery. 1 Nevertheless, the few studies that have looked at the impact of maternal age in community context suggest that geographic variations in magnitude of the maternal age effect may provide clues to the presence of exposures in certain populations that erode reproductive health outcomes over the childbearing years, possibly shedding light on the causes of racial disparities at all ages. For example, Geronimus reported that the effect of maternal aging on birthweight (weathering) is magnified among African American women who reside in low-income, as compared with high-income, urban areas, 19 suggesting that the impact of maternal age on birth outcomes may depend on some underlying processes associated with social or residential context. Findings such as these have prompted researchers to employ contextualized, multilevel analytic strategies to take into consideration social-structural influences on health. 30– 33 In one of the few perinatal studies that used multilevel modeling techniques, O'Campo et al. 34 demonstrated that associations between individual risk factors and LBW were moderated by neighborhood characteristics. Specifically, the adverse impact of older maternal age on infant birthweight was more pronounced under community conditions of high unemployment. The present study was undertaken to explore the impact of maternal age on infant birthweight under varying community conditions while taking into consideration the role of individual risk factors. Specifically, we aimed to clarify the contribution of maternal age to the likelihood of moderately low birthweight (MLBW) and VLBW among African American and White women living in a major urban area and to determine whether the association between older maternal age and low birthweight depends on community conditions.
