Prenatal diffusion-weighted MRI in growth-restricted fetuses: early diffusion changes beyond Doppler findings: a retrospective cohort study

Although fetal growth restriction (FGR) and small for gestational age (SGA) both denote impaired fetal growth, they are distinct clinical entities defined by different diagnostic criteria. FGR is primarily associated with placental insufficiency and chronic hypoxia, which may result in progressive cerebral injury even before overt clinical manifestations become apparent. However, direct comparisons of brain diffusion characteristics between FGR and SGA fetuses remain limited. To evaluate fetal brain diffusion changes in growth-restricted (FGR) and small-for-gestational-age (SGA) fetuses using diffusion-weighted magnetic resonance imaging (DW-MRI), and to correlate findings with Doppler ultrasound parameters. In this retrospective study, we included singleton pregnancies diagnosed with FGR or SGA who underwent fetal brain MRI after 30 weeks of gestation. FGR was defined based on estimated fetal weight or abdominal circumference <10th percentile with abnormal Doppler indices, while SGA fetuses had similar biometric criteria but normal Dopplers. Apparent diffusion coefficient (ADC) values were measured in eleven brain regions including frontal and occipital white matter, thalami, centrum semiovale, pons, and cerebellar hemispheres and compared between FGR and SGA groups. Doppler indices and perinatal outcomes were also analyzed. A total of 44 patients (30 FGR, 14 SGA) were included. FGR fetuses had significantly higher umbilical artery pulsatility index, smaller biparietal and transverse cerebellar diameters, and lower ADC values in frontal white matter compared to SGA fetuses. ADC values in other brain regions were not significantly different. Lower 1-minute Apgar scores, lower cord pH values, and higher NICU admission rates were more frequent in the FGR group. DW-MRI may identify early brain alterations in FGR fetuses before overt clinical signs. Combined with Doppler findings, MRI can enhance risk stratification and guide timing of delivery.