Objective: To investigate whether periconceptional maternal intake of ultra-processed foods (UPF) impairs first-trimester utero-placental vascular development, and whether macronutrients and dietary patterns substantiate the associations. Design: Prospective observational cohort. Setting: Academic hospital. Population or Sample: Ongoing pregnancies. Methods: 93 women completed a food frequency questionnaire from which we calculated percentage of energy intake from UPF, intake of energy and macronutrients and adherence to dietary patterns. We performed sequential three-dimensional power Doppler ultrasounds of the first-trimester utero-placental vasculature. VOCAL software, Virtual Reality segmentation and a skeletonization algorithm were applied to measure placental volume (PV), utero-placental vascular volume (uPVV) and generate the utero-placental vascular skeleton (uPVS). Absolute vascular morphology was quantified by assigning a morphologic characteristic to each voxel in the uPVS (end-, bifurcation-, crossing- or vessel point) and used to calculate density of vascular branching. Main Outcome Measures: PV, uPVV, uPVS characteristics and density of vascular branching. Results: Fully adjusted linear mixed models showed a 10%/day higher UPF intake was associated with increased first-trimester density of vascular branching (bifurcation points: β=0.465√n, 95%CI=0.148;0.782). Higher carbohydrate intake of 10g/day was associated with increased trajectories of uPVV (β=0.017, 95%CI=0.001;0.032) and uPVS (end points (β=0.286, 95%CI=0.062;0.511), bifurcation points (β=0.004, 95%CI=0.003;0.006), vessel points (β=0.772, 95%CI=0.137;1.408). The associations were substantiated by the adherence to the “Snack” dietary pattern. Conclusions: Periconceptional maternal intake of UPF is associated with impaired first-trimester utero-placental vascular development, whereas the intake of carbohydrates and strong adherence to a ‘Snack’ dietary pattern, is positively associated with first-trimester utero-placental vascular development.