biomedical and other psychosocial factors were controlled for. The chronic stress measures contained 12 items that assessed financial, family, work, health, and other forms of ongoing stress.
In sum, studies of chronic and catastrophic stress exposures are suggestive of an association between stress and preterm birth, although the findings are not yet definitive. Such studies offer an opportunity to use quasiexperimental designs instead of correlational designs, and these quasiexperimental studies may add to the ability to draw inferences (Cook and Campbell, 1979; Shaddish et al., 2002), and also have the potential to test competing theories about acute versus chronic stress exposures and their effects on preterm birth.
The early research on psychosocial risk factors for preterm delivery and low birth weight focused on maternal anxiety (Gorsuch and Key, 1974). Other studies over the years have focused on the role of general distress. Determination of whether either depression or anxiety is a risk factor for preterm delivery has, however, been difficult for many reasons. Among these is the fact that the two emotional states are often comorbid, although they are distinguishable clinically. However, the questionnaire measures used in obstetric research to assess anxiety and depression are not well suited to their differentiation. Thus, many studies have investigated general distress by using the General Health Questionnaire (Hedegaard et al., 1993, 1996; Perkin et al., 1993) or the Hopkins Symptom Checklist (Paarlberg et al., 1996). General emotional distress may not be as clear-cut a risk factor as the potentially separable effects of either anxiety or depression.
Recent studies suggest that anxiety may be a potentially important risk factor for preterm delivery. The IOM committee found 12 studies in total that tested the emotional components of stress as predictors of preterm birth. Eleven studies had prospective designs; of these, nine tested the association of anxiety with gestational age or preterm birth. Two found no significant effects for state anxiety (Lobel et al., 2000; Peacock et al., 1995); one study found that general anxiety was associated with intrauterine growth restriction (but not with preterm birth), but only in white patients (Goldenberg et al., 1996a); and one study found that general anxiety was associated with preterm labor in women who had a history of preterm labor (Dayan et al., 2002).
Four more investigations were very consistent in finding that anxiety concerning the pregnancy itself was associated with gestational age or preterm birth. For example, Rini et al. (1999) reported that prenatal anxi-