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FIGURE 2-3 Global prevalence of preterm births, 2010.
SOURCE: Blencowe et al. (2012, Figure 3).

2009). Indeed, country rankings remained identical even when Palloni and Yonker (2012) recalculated the rates to exclude preterm births (less than 22 weeks of gestation).

Infant mortality and low birth weight are both markers of unhealthful in utero and postnatal conditions, findings that are also supported by related indicators. From birth through age 4, U.S. children lose more years of life than children in the other 16 peer countries (Palloni and Yonker, 2012). Infants who die during the first year of life, particularly preterm infants, are those at the lower tail of the distribution of newborns by health status, and low-birth-weight babies are at the extreme end of this tail. Both infant mortality and low birth weight are, in turn, influenced by maternal characteristics, including health-related behaviors (e.g., smoking, drinking, diet, and breastfeeding practices), marital and family status, maternal education, access to health care, and household and family conditions. The U.S. excess in infant mortality and the prevalence of low-birth-weight babies probably reflect both individual and societal contextual factors. For example, the United States fares poorly with respect to adolescent pregnancy and child poverty (see Chapter 6), which are, respectively, proximate and distal determinants of low birth weight and infant mortality.

Data are available to track trends over time in U.S. infant mortality and birth weight relative to other countries. By the early 1960s, the average infant mortality rate among peer countries had dropped to the U.S. rate, and by the 1970s the United States began to develop a disadvantage in infant mortality (Viner, 2012) (see Figure 2-4). Although U.S. infant



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