Introduction: Our aim was to assess placental function by diffusion-weighted magnetic resonance imaging (MRI) using intravoxel incoherent motion (IVIM) analysis in uncomplicated pregnancies and pregnancies complicated by placental dysfunction. Methods: 31 normal pregnancies and 9 pregnancies complicated by placental dysfunction (birthweight ≤ -2SD and histological signs of placental vascular malperfusion) were retrieved from our placental MRI research database. MRI was performed at gestational weeks 20.1–40.6 in a 1.5 T system using 10 b-values (0–1000 s/mm2). Regions of interest were drawn covering the entire placenta in five transverse slices. Diffusion coefficient (D), pseudodiffusion coefficient (D*) and perfusion fraction (f) were estimated by IVIM analysis. Results: In normal pregnancies, placental f decreased linearly with gestational age (r = −0.522, p = 0.002) being 26.2% at week 20 and 18.8% at week 40. D and D* were 1.57 ± 0.03 and 31.7 ± 3.1 mm2/s (mean ± SD), respectively, and they were not correlated with gestational age. In complicated pregnancies, f was significantly reduced (mean Z-score = −1.16; p = 0.02) when compared to the group of normal pregnancies, whereas D and D* did not differ significantly between groups. Subgroup analysis demonstrated that f was predominantly reduced in dysfunctional placentas characterized by fetal vascular malperfusion (mean Z-score = −2.11, p < 0.001) rather than maternal vascular malperfusion (mean Z-score = −0.40, p = 0.42). In addition, f was negatively correlated with uterine artery pulsatility index (r = −0.396, p = 0.01). Discussion: Among parameters obtained by the IVIM analysis, only f revealed significant differences between the normal and the dysfunctional placentas. Subgroup analysis suggests that placental f may be able to discriminate non-invasively between different histological types of vascular malperfusion.