PURPOSEWe aimed to compare the placental diffusion difference between intrauterine growth restriction(IUGR) patients with worsening Doppler ultrasonography (US) findings and control group withnormal Doppler US findings by using diffusion-weighted imaging (DWI).METHODSWe performed a prospective study to compare the placental diffusion difference in 63 patients(gestational week, 28–34 weeks), including 50 IUGR patients (mean gestational week, 30 weeks3 days ±16.2 days) with worsening Doppler US findings and 13 patients with normal Doppler USfindings (mean gestational week, 29 weeks 4 days ±12.3 days) by using DWI (b value, 0–1000 s/$mm^2$). We classified IUGR patients into three groups according to the reference values of the umbilical artery pulsatility index (PI) chart. Placenta apparent diffusion coefficient (ADC) calculationswere performed by freehand drawn regions-of-interest (ROIs) (min, 8.04 $cm^2$; max, 200 $cm^2$).RESULTSPlacental ADC values in IUGR patients (mean, 1.624±0.181 ×10–³ mm²/s; range, 1.35–1.96 ×$10^{-3}$$mm^2$/s) were significantly reduced compared with the control group (mean, 1.827±0.191 ×10–³mm²/s; range, 1.35–2.84 ×$10^{-3}$ $mm2^$/s) (P = 0.001). For adjusted ROI area calculation, ADC valueswere significantly lower in groups 3, 2 and 1, respectively, compared with the control group (P <0.05); and there was no significant difference between groups 1 and 2 (P > 0.05). Preeclampsiasignificantly reduced the placental diffusion compared with patients without preeclampsia (P =0.003). Gestational aging did not significantly affect ADC values in control patients (r=0.08, P =0.561). The sensitivity, specificity, negative and positive predictive values of ADC to detect IUGRwere 72%, 84.6%, 44%, and 94.7% with a cutoff value of 1.727 ×$10^{-3}$ $mm2^$/s, respectively.CONCLUSIONThe diagnostic estimation of placental ADC values to predict the severity of IUGR is comparableto that of umbilical artery PI. Considering that at the very early onset of IUGR, placental diffusiondiminishes, ADC as a marker for IUGR in lieu of umbilical artery PI has the potential to determinethe threshold for decreased placental diffusion. Therefore, DWI should be added to routine fetalMRI to show diffusion changes in placenta.