Background: Although maternal employment is considered a risk factor for low birth weight (LBW), the manner in which employment might affect birth weight is poorly understood. In this analysis, selected characteristics of employment during pregnancy were examined for effects on pregnancy outcomes. Methods: Work characteristics included the number of hours per week, physical activities, and environmental conditions. The outcomes of interest were fetal growth retardation (<2500 grams at term) and preterm delivery (<37 weeks). The study population consisted of 2711 non-Black, married mothers who participated in the 1980 National Natality Survey (NNS). The NNS data were merged with data from the 1m revision of The Dictionary of Occupational Titles (DOT) from which measures of occupational physical activities and environmental exposures were obtained. Logistic regression was used in the analysis. Results: Those who worked 40 or more hours per week were more likely than women who worked fewer hours to have a low birth weight delivery at>=37 weeks. No physical or environmental characteristics of work were associated with low birth weight or preterm delivery. Conclusions. Non-Black married American women may face a risk of delivering low-birth weight babies at or near term only if they work 40 or more hours each week. However, the lack of risk associated with other characteristics of work may be a function of measurement error in the DOT data source or of low levels of exposure in the analysis population. (Am J Public Health. 1991; 81;1007-1012).