300 nonsmoking women in New York City who were pregnant at the time. Women who were in the first trimester at the time of the attack delivered infants of significantly shorter gestations, and women whose place of employment was within 2 miles of the World Trade Center had marginally shorter gestations. Strikingly similar effects were found by Glynn and colleagues (2001), who examined gestational age at delivery of 40 women who experienced a major earthquake in the first, second, or third trimester or postpartum. They found a significant effect of the timing of the earthquake during pregnancy on gestational age, such that the later in pregnancy that an earthquake occurred, the longer the gestation was. The longest gestational age in that study was among women who had already delivered at the time of the event (and who were effectively unexposed), and the shortest gestation was among women who experienced the earthquake in the first trimester. Although the sample size was small and some alternative explanations cannot be ruled out, these results are intriguing, especially because of their similarity to those of Lederman et al. (2004), as they indicate that the timing of sudden traumatic environmental stressors during pregnancy may affect the timing of delivery. Although the methodological strengths of these studies vary, they avoid some of the pitfalls encountered in life events approaches because all the participants in the studies experienced the same stressor.⁴

Turning to more chronic forms of exposure, Stein et al. (2000) studied 237 homeless women interviewed at 78 shelters or meal programs. The severity of homelessness, especially the variable of the percentage of the woman’s lifetime that she had been homeless, predicted both preterm birth and low birth weight (each of which controlled for the other). The analyses controlled for many other variables, such as substance use, trauma and distress, prior birth complications, race-ethnicity, income, and various medical risk factors. The severity of homelessness is a fairly objective measure of chronic stress or strain and not merely a measure of perceived stress or distress; but it may have been confounded nonetheless by inadequate nutrition or general health neglect, as the authors point out, which could account in part for these effects. Nonetheless, these are unique findings on the possible role of chronic stress in preterm birth and low birth weight.

Misra and colleagues (2001) also retrospectively studied chronic stress during pregnancy in 739 low-income African-American non-Hispanic women interviewed after delivery. Multivariate analyses indicated that chronic stress predicted preterm delivery (adjusted OR = 1.86) when several