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ment of hypothesized pathways to preterm birth as a basis for any future study of these factors. In addition, the study of these factors in combination with social factors, such as race and ethnicity, social class, and neighborhood factors (see Chapter 4), is recommended.

Intendedness of Pregnancy and Preterm Delivery

The term unintended refers to those pregnancies that are unwanted or mistimed (i.e., they occur earlier than desired by the parents). Intentions are measured by self-report by using standard survey questions that can distinguish between whether the woman wanted a child now, not now but at some point (mistimed), or not at all (unwanted). These questions are answered after conception and in many studies are answered after delivery, which may introduce retrospective bias.

It is estimated that approximately 60 percent of all pregnancies are unintended, and of these, about half end in a live birth (IOM, 1995). Women with unintended pregnancies are less likely to seek early prenatal care (Bitto et al., 1997; IOM, 1995; Kost et al., 1998; Pagnini and Reichman, 2000) and are more likely to use alcohol or tobacco (IOM, 1995). They also appear to be more likely to experience high levels of exposure to psychosocial stress and depressive symptoms (Orr and Miller, 1997). Although unintended pregnancies occur among women across the sociodemographic spectrum, they are disproportionately likely among mothers who are adolescent, unmarried, or over age 40 (Bitto et al., 1997; IOM, 1995). The child of an unwanted pregnancy (as opposed to the child of a wanted or a mistimed pregnancy) is at greater risk of low birth weight, death in the first year of life, abuse, and receiving insufficient resources for optimal early child development (IOM, 1995). Additional consequences occur for the parents of unwanted pregnancies. For example, a study that used data from the Pregnancy Risk Assessment Monitoring System database of 39,348 women in 14 states who delivered a live-born infant (Goodwin et al., 2000) found that women with unintended pregnancies had a 2.5 times greater risk of physical abuse.

Having an unintended pregnancy is estimated to increase the odds of delivering an infant of low birth weight by about 1.2 to 1.8 (IOM, 1995). However, only three studies on intentions and preterm birth were available as of 1995, and of those three studies, two were unpublished. On the basis of the findings from these preliminary studies, IOM (1995) indicated that the increased risk of low birth weight because of an unintended pregnancy appeared to be related to preterm delivery rather than intrauterine growth restriction. Subsequently, at least one further study has been conducted with a sample of 922 African American, low-income pregnant women recruited in four hospital-based prenatal clinics in Baltimore, Maryland (Orr et al.,

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