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BACKGROUND Multiecho gradient-echo Cartesian MRI characterizes placental oxygenation by quantifying R2* . Previous research was performed at 1.5T using breath-held 2D imaging during later gestational age (GA). PURPOSE To evaluate the accuracy and repeatability of a free-breathing (FB) 3D multiecho gradient-echo stack-of-radial technique (radial) for placental R2* mapping at 3T and report placental R2* during early GA. STUDY TYPE Prospective. POPULATION Thirty subjects with normal pregnancies and three subjects with ischemic placental disease (IPD) were scanned twice: between 14-18 and 19-23 weeks GA. FIELD STRENGTH 3T. SEQUENCE FB radial. ASSESSMENT Linear correlation (concordance coefficient, ρc ) and Bland-Altman analyses (mean difference, MD) were performed to evaluate radial R2* mapping accuracy compared to Cartesian in a phantom. Radial R2* mapping repeatability was characterized using the coefficient of repeatability (CR) between back-to-back scans. The mean and spatial coefficient of variation (CV) of R2* was determined for all subjects, and separately for anterior and posterior placentas, at each GA range. STATISTICAL TESTS ρc was tested for significance. Differences in mean R2* and CV were tested using Wilcoxon Signed-Rank and Rank-Sum tests. P < 0.05 was considered significant. Z-scores for the IPD subjects were determined. RESULTS FB radial demonstrated accurate (ρc ≥0.996; P < 0.001; |MD