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2000). Women with unintended pregnancies were 1.82 times more likely to deliver their infants preterm, after adjustment for clinical and behavioral factors associated with preterm delivery.

Thus, although the research available on the association of the intendedness of pregnancy and preterm delivery is limited, that which is available suggests that women with unintended pregnancies are more likely to deliver preterm, and as a consequence, their infants are at higher risk of being of low birth weight. Understanding the pathways from unintended conception to preterm labor and delivery by the use of multilevel approaches would be useful in elucidating the etiology of preterm birth for at least some subgroups of women. Unmeasured socioeconomic factors that may be confounded with unintended pregnancies must be carefully controlled in future studies. In addition, it is critical to refine measures of intendedness to be sure they are valid and reliable if this arena of research is to be pursued. Reducing unintended pregnancies through family planning and other mechanisms could indirectly reduce the rates of preterm delivery and related adversities (IOM, 1995). Disparities in pregnancy outcomes, including preterm birth, could also be reduced by paying attention to the intendedness of a pregnancy (Hogue and Vasquez, 2002).

SUMMARY AND FUTURE DIRECTIONS FOR RESEARCH

Among the behavioral and psychosocial factors considered, the one that shows the most consistent evidence of having an adverse impact on the risk of preterm birth is cocaine use. Dietary constituents have been examined to a limited degree, with mixed evidence on the potential benefits of increased levels of iron, long-chain fatty acids, folate, and vitamin C being found. Although none of these dietary constituents is well established as having effects that prevent preterm birth, all warrant further evaluation. Leisure time physical activity has been associated with a reduced risk of preterm birth, but the implications for causality are unclear. Employment alone is nonspecific as a factor related to preterm birth, and meaningful etiologic research of this association is likely not possible. Although vaginal douching is of interest as a cause of preterm birth, given the concern with reproductive tract infections and the different prevalences of such infections between African American and white women, evidence of an influence on preterm birth is lacking thus far.

The evidence is fairly consistent that the occurrence of large numbers of major life events and the experiencing of severe life events during pregnancy are associated with preterm birth. Studies of chronic and catastrophic stress exposures are fewer in number, but such exposures also appear to contribute to preterm delivery, although more research in this area is needed. Past research findings are also consistent in pointing to maternal anxiety, espe-



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