Establishment of Normal ADC Values and Morphological Parameters of the Fetal Kidney Using Magnetic Resonance Imaging and Analysis of their Correlation with Gestational Age

Background Fetal renal developmental abnormalities are among the most common congenital malformations and are associated with adverse perinatal outcomes. However, existing fetal magnetic resonance imaging (MRI) studies are limited by small sample sizes and the lack of comprehensive gestational age (GA)–specific reference ranges that integrate both morphological and functional parameters. This study aimed to establish multiparametric MRI reference ranges for normal fetal kidneys and to characterize their relationships with GA. Methods In this retrospective single-center observational study, 313 singleton pregnancies (GA 23–39 weeks) with normal postnatal urinary outcomes underwent 1.5T fetal MRI, including T2-weighted and diffusion-weighted imaging sequences. Morphological parameters [anteroposterior, transverse and longitudinal diameters, and mean renal parenchymal thickness (MRPT)] and functional parameters [T2 relative signal intensity (RSI-T2) and apparent diffusion coefficient (ADC)] were measured for both kidneys. Reproducibility was assessed using intraclass correlation coefficients (ICC). Correlations between MRI parameters and GA were analyzed, and linear regression models were constructed for ADC. Results All morphological and functional parameters demonstrated good to excellent intra- and inter-observer reproducibility (ICC > 0.75). Renal diameters and MRPT increased significantly with GA (r = 0.72–0.89; all P < 0.0001), reflecting progressive macroscopic growth. In contrast, ADC values decreased moderately with advancing GA (right kidney: r = − 0.47; left kidney: r = − 0.52; both P < 0.0001), consistent with microstructural and functional maturation. The regression equations for ADC (×10⁻³ mm²/s) were: ADC_right = 3.23 − 0.049 × GA and ADC_left = 3.46 − 0.058 × GA. Conclusions This study provides GA-stratified reference ranges for key morphological and functional MRI parameters of normal fetal kidneys in the second and third trimesters. These quantitative benchmarks may improve prenatal assessment of fetal renal growth and maturation and support earlier detection and characterization of fetal renal developmental abnormalities. Trial registration Not applicable.