influenced by different environmental factors over time, and that many areas of family well-being are affected. The prevalence of neurodevelopmental disabilities and health impairments varies. This is not surprising, in light of the multiple etiologies and complications of preterm birth and the variability of both the intrauterine and the extrauterine environments to which fetuses and children born preterm are exposed. In recognition of the increased developmental and emotional risks of children born preterm, several interventions have focused on the provision of services in the early years of life to prevent subsequent developmental and health problems. Although early interventions have a short-term impact, it has been more difficult to demonstrate more long-term benefits.
At first glance, a wealth of data seems to be available for characterization of the outcomes of infants born preterm; however, as with many other areas addressed in this report, much of this literature uses birth weight as the measure of prematurity (see Chapter 2). The use of birth weight as a selection criterion for studies of the outcomes for infants born preterm introduces a well-recognized bias by including various proportions of more mature infants who experienced intrauterine growth retardation (IUGR). Many infants with IUGR are small for gestational age when they are born full term (i.e., at 37 to 41 weeks of gestation). Most infants with birth weights of less than 1,500 grams are preterm, but those who also have IUGR are vulnerable to the complications of both IUGR and prematurity (Garite et al., 2004). A number of the more recent studies have reported on the outcomes for preterm infants by gestational age category, but as in other parts of this report, this chapter uses birth weight-specific data when information by gestational age is not available.
Finding 11-1: Most studies of the outcomes of preterm birth use birth weight criteria for the selection of study participants. Few studies report on the outcomes for preterm infants by gestational age. In addition to infants born preterm, studies with samples of infants with birth weights less than 2,500 grams include full-term infants who are small for gestational age.
When this literature is examined, it is also well to keep in mind that preterm delivery is not a disease with a fixed set of outcomes. Rather, preterm delivery increases the risk of adverse outcomes that are also seen in term infants. Nevertheless, the more preterm an infant is, the greater the risk of adverse outcomes. Thus, these outcomes are a probability for a group