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Abstract: Background: Previous research suggests that prenatal maternal stress (PNMS) impacts birth outcomes, but many human studies cannot distinguish between the effects of different types of stressors or examine effects of exposure timing on outcomes. Objectives: Our goal was to determine how timing and severity of exposure during pregnancy to objective and subjective stress due to a natural disaster influenced gestation length and fetal growth patterns. Methods: We assessed objective and subjective PNMS levels among 172 women exposed to an ice storm during or shortly before pregnancy. We analyzed associations between PNMS levels and outcomes (gestation length, birth weight, birth length, head circumference, and growth ratios), controlling for other variables such as age, obstetric complications, socioeconomic status, and trait anxiety. Results: Gestation lengths and predicted birth weights were shorter among participants exposed to the ice storm during early to mid pregnancy, compared to 3rd trimester and pre-pregnancy exposure. Birth lengths were shorter in the sample compared to population references, and predicted values were shorter among participants with a “discrepancy” between their objective and subjective PNMS levels. High objective PNMS levels predicted smaller head circumferences in early pregnancy, but we also observed patterns in predicted values of head circumference to birth length ratios suggesting the sparing of brain development relative to birth length among boys in early pregnancy. These sparing effects decreased in later pregnancy. Conclusions: Exposure to stressful events during pregnancy influences birth outcomes independently of other factors. Exposure timing, newborn sex, and the type of stressor influence the effects observed. [Copyright &y& Elsevier]