Obesity during pregnancy has major consequences for maternal and neonatal health, but the long-term effects on the offspring are less clear. It is not known whether the effects observed in animal models are a result of maternal obesity per se or of the high-fat diets used to induce obesity. This investigation aimed to develop a model for the evaluation of the independent effects of cafeteria feeding and maternal obesity, considering their impact on plasma volume expansion, circulating metabolites, and fetal and placental growth. Wistar rats were fed a control or cafeteria diet from weaning. After 8 weeks, all animals were mated and half of the animals within each group were crossed-over to the alternative diet. This generated four treatment groups, differing in their pre-gestational and gestational diets. Half of the animals were culled at day 5 of gestation and the remainder at day 20. Maternal body composition, blood volume and circulating glucose, TAG and cholesterol were determined. Cafeteria feeding was effective in inducing obesity, as demonstrated by increased fat depot weights and total body fat, without impacting upon reproductive success or circulating lipid concentrations. The study successfully demonstrated that there were differential effects of maternal body fatness and diet upon fetal and placental growth, with pre-gestational obesity leading to lower fetal weight at day 20 of gestation (P < 0·001). The model will provide a useful vehicle for the investigation of the complex interactions between dietary- and obesity-related factors during pregnancy in their effects on fetal development and postnatal metabolic function.