In order to determine whether pregnancy outcome was altered when women were employed outside their homes, 7,722 pregnancies were analyzed. Gestations were not shortened but newborns of women who worked in the third trimester weighed 150 to 400 gm less than newborns of mothers who remained at home. The growth retardation was greatest when women were underweight pregravid and had a low pregnancy weight gain, when they were hypertensive, or when the work required standing. The growth retardation remained after the data were stratified by race, socioeconomic status, and other maternal factors that commonly influence fetal growth. The frequency of large placental infarcts progressively increased when women continued stand-up work into late gestation. Such infarcts reached a peak of 250/1,000 births after the 37th week of gestation in stand-up workers. Low uteroplacental blood flow is a likely explanation for both the fetal growth retardation and the large placental infarcts.

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