United States (the Pregnancy Risk Assessment Monitoring System) by assessing life events 2 to 6 months after delivery (retrospectively). Experiencing more than two life events predicted preterm birth in primiparous pregnancies in one cohort (1994 and 1995), and more than five life events predicted preterm birth in multiparous pregnancies in the other cohort (1990 to 1993). Why these results did not cross replicate across cohorts is unclear (also see the findings of Lu and Chen , based on a third cohort from the same study).
However, the results presented above are consistent with those of two additional studies restricted to African-American women. In one study, the number of prenatal major life events, as assessed prospectively, was associated with gestational age in a sample of 179 pregnant women selected from a larger data set (Parker Dominguez et al., 2005). The other study of African-American women (Collins et al., 1998), which had a case-control design, indicated that three or more life events in pregnancy were significantly associated (OR = 3.1) with very low birth weight (all cases were also preterm births; see also Sable and Wilkenson ). Zambrana et al. (1999) also found a bivariate association between life events and gestational age in a large sample of women of Mexican origin or descent and African-American women studied in the second trimester. However, the strongest effect in that study was detected when life events were combined with other stress measures into a latent factor in a multivariate model.
Thus, there is some consistent evidence that major life events are associated with preterm birth, although the evidence is by no means uniform. High numbers of life events and severe life events or life events with the greatest impact have been more consistently predictive of preterm birth across studies.3 On the whole, the focus in the future should be on approaches to the study of life events that delineate events by their severity and emphasize those with the highest negative impacts.
A second set of studies involved a common chronic stressor, such as being imprisoned (Hollander, 2005) or homeless (Stein et al., 2000) during pregnancy or experiencing a catastrophic event occurring during pregnancy (Glynn et al., 2001; Lederman et al., 2004). For example, Lederman and colleagues (2004) assessed the impact of the time of gestation at the time of the World Trade Center terrorist attack on September 11, 2001, among