PIP: This discussion explores the relationship between maternal nutrition and duration of gestation. From most published research, it is unclear whether the effects of nutrition on infant size are, in part, due to associations of maternal nutrition with the duration of gestation. Fetal growth is strongly related to maternal weight, height, plasma volume, and other indices that reflect maternal size both at conception and during gestation. These indices in part reflect current nutritional status, but they also are determined by other factors, such as genetic predisposition and general health status. There are reliable data on associations between maternal height, weight, and skinfold thickness and duration of gestation. As a whole, these studies fail to support the hypothesis that maternal nutritional status at conception or in early pregnancy is other than very weakly associated with duration of gestation. There are few marked effects of acute or chronic calorie deprivation or supplementation on duration of gestation, at least among pregnancies that have been carried to the 3rd trimester. Poor women living under chronically deprived conditions bear infants of lower birth weight than more affluent women, but this appears to be primarily mediated by depressed fetal growth. Large differences exist in mean gestation associated with social differences, at least in some groups (American blacks compared with American whites; lower classwomen in the British perinatal study), but such differences can hardly be assumed to arise only from differences in nutrition. The results of supplementation studies suggest that real, but small, gains in duration of gestation are possible through dietary intervention.