Gestational age-specific MRI reference values for fetal renal morphology and ADC

BACKGROUND: Fetal renal developmental abnormalities are among the most common congenital malformations and are associated with adverse perinatal outcomes. Although fetal magnetic resonance imaging (MRI) can provide complementary morphological and quantitative information, gestational age (GA)-specific reference values integrating fetal renal morphology and diffusion parameters remain limited. This study aimed to establish MRI-based reference values for normal fetal renal morphology and apparent diffusion coefficient (ADC) across gestation. METHODS: In this retrospective single-center observational study, 313 singleton pregnancies (GA 23-38 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). Associations between MRI parameters and GA were evaluated using correlation and linear regression analyses. RESULTS: 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 provide a reference framework for fetal renal MRI assessment and for future studies of fetal renal abnormalities. TRIAL REGISTRATION: Not applicable.