OC02.06: Assessment of placental perfusion and volume with MR IVIM model and correlation with fetoplacental Doppler in late‐onset fetal growth restriction

To assess placental perfusion and volume through magnetic resonance (MR) and Intra-Voxel Incoherent Motion (IVIM) model and to examine their associations with fetoplacental Doppler in late-onset fetal growth restriction (FGR) pregnancies. Prospective cohort study of singleton pregnancies, involving 28 late-onset FGR and 131 normally grown fetuses. Third trimester ultrasound scans (29-34 weeks) were performed to evaluate fetoplacental Doppler. A placental MR, employing both T2-weighted and diffusion-weighted images (DWI), was performed at 36-38 weeks. The DWI utilised 10 b-values (from 0 to 1000 s/mm2), measuring perfusion fraction (f) and diffusion coefficient (D) with ivim.sav software in seven slices near the umbilical cord insertion. Placental volume was obtained through manual delineation using the Fiji software. In FGR pregnancies, placental volumes were significantly reduced compared to controls (747.66cm3 vs. 963.04cm3, p < 0.01), showing significant correlations with birthweight (r = 0.571, p < 0.01) and birthweight centile (r = 0.543, p < 0.01). Moreover, there was a significant association between placental volume and uterine artery mean pulsatility index (PI) Z-score (r = -0.316, p < 0.001), but no correlations were detected with f (r = 0.05, p = 0.5) or D (r = 0.07, p = 0.34). Growth-restricted pregnancies showed no differences in f and D compared to controls (f 39% vs. 39.5%, p = 0.8; D 1410.4 mm2/s vs. 1453.8 mm2/s, p = 0.38). Additionally, no significant correlation was found between f and uterine artery mean PI Z-score (r = -0.10, p = 0.19). While a correlation exists between placental volume and key parameters such as fetal growth and uterine artery Doppler, MR IVIM perfusion parameters may not be useful in assessing placental insufficiency. Larger sample sizes are needed to confirm these findings.