Background: The prenatal environment can induce permanent changes in offspring phenotype. Thinness at birth is associated with adult risk of cardiometabolic disease. Objective: The objective was to investigate the association between maternal nutrition during pregnancy and intrauterine development of fetal body composition. Design: We used prospective data from 179 Australian women with singleton pregnancies from the Women and Their Children's Health Study. A validated food-frequency questionnaire was used at 18–24 wk and 36–40 wk of gestation to quantify maternal diet during the previous 3 mo of pregnancy. Fetal body-composition measurements were ascertained from abdominal and midthigh sites by ultrasound performed at 19, 25, 30, and 36 wk. The subcutaneous fat area at each site was calculated by subtracting the lean/visceral area from the total area. Results: In linear mixed-model regressions, maternal intakes of protein (b = −0.13; P = 0.04) and starch (b = 0.10; P = 0.02) and the protein:carbohydrate ratio (b = −3.61; P = 0.02) were associated with the percentage of abdominal fat, whereas SFA (b = 0.27; P = 0.04) and PUFA (b = −0.48; P = 0.03) were associated with the percentage of midthigh fat. Response surfaces for fetal adiposity were maximized at different macronutrient intakes. Abdominal fat was highest with low protein intakes (<16% of energy), and midthigh fat was highest at intermediate protein (18–21% of energy), high fat (>40% of energy), and low carbohydrate (<40% of energy) intakes. Conclusion: Fetal body composition may be modifiable via nutritional intervention in the mother and thus may play an important role in influencing the offspring's risk of future disease.