Fatimah Al Darwish

Placental insufficiency refers to a placenta-centered failure to establish or maintain sufficient maternal–fetal exchange. It underlies key obstetric complications, especially preeclampsia (PE) and fetal growth restriction (FGR). In clinical practice, assessment of placental function remains largely indirect, relying on fetal biometry and Doppler indices rather than direct measures of perfusion and oxygenation. In parallel, there is still no widely effective therapy that restores placental function once insufficiency is established. As a result, management frequently focuses on surveillance and timing of delivery. These limitations underscore the urgent need for functional biomarkers that can measure placental oxygenation and perfusion in vivo, across gestation. This thesis aimed to advance a mechanistic, time-specific understanding of placental insufficiency in the reduced uterine perfusion pressure (RUPP) rat model by integrating in vivo functional imaging readouts of placental perfusion and oxygenation with biological readouts of uteroplacental remodeling. Across the experimental chapters, magnetic resonance imaging (MRI), including T2* mapping and 3D dynamic contrast-enhanced MRI (3D DCE-MRI), was complemented by contrast-enhanced ultrasound (CEUS), photoacoustic imaging (PAI), and histology of the maternal–fetal interface to map how functional and structural components of placental insufficiency evolve over gestation. Chapter 2 provides the clinical and translational rationale by reviewing molecular and imaging biomarkers linked to placental hypoxia and insufficiency. The chapter highlights that molecular tissue biomarkers are typically available only after delivery, while circulating biomarkers in maternal blood are proxies rather than direct readouts of placental function. Non-invasive imaging, therefore, emerges as a promising method to monitor placental function longitudinally, and as a bridge between biology and clinically relevant biomarkers. Chapter 3 establishes quantitative late-gestation MRI readouts in the RUPP model at gestational day (GD) 19. T2* mapping showed reduced placental T2* in RUPP pregnancies in both the labyrinth and junctional zone, indicating reduced placental oxygenation, while fetal brain and liver T2* values remained comparable between groups. In contrast, semi-quantitative 3D DCE-MRI parameters did not differ between RUPP and controls at this time point. Together, these results demonstrate a dissociation between oxygenation and perfusion readouts late in gestation and suggest that oxygenation sensitive measures may reveal placental compromise even when perfusion metrics appear preserved. Chapter 4 shows how RUPP influences key maternal–fetal interface processes over time (GD14, GD16, GD18, and GD19). Gross placental macro-architecture was preserved, but the processes that normally remodel the uterine vasculature into a high-capacitance, low-resistance system were persistently impaired. Specifically, uNK cell migration from the mesometrial triangle was disrupted with sustained uNK cell presence, trophoblast invasion depth was reduced, and spiral artery remodeling was impaired, with a shift towards unremodeled or only partially remodeled arteries by late gestation. These findings identify a durable structural and immunovascular maladaptation that can constrain functional reserve. Chapter 5 resolves the temporal dynamics of perfusion impairment after RUPP using longitudinal 3D DCE-MRI from GD14 to GD18. Immediately after surgery (GD14), RUPP placentas showed delayed time-to-peak, reduced maximum enhancement, reduced wash-out, and elevated early AUC, consistent with restricted inflow and impeded transit. By GD15, abnormalities persisted for a subset of parameters, but by GD16–GD18 group-level differences in semi-quantitative perfusion metrics were no longer detectable, indicating substantial hemodynamic adaptation. Importantly, exploratory voxel-wise histogram analyses revealed marked intra-litter heterogeneity, with a subset of RUPP placentas deviating clearly from a normal pregnancy template. Together, these results identify GD14–GD15 as a critical window for detecting acute perfusion impairment and for evaluating interventions targeting early injury mechanisms, while also emphasizing the need to quantify heterogeneity beyond placenta-averaged metrics. Chapter 6 extends the functional characterization to a multimodality setting at mid-gestation (GD16) by combining MRI (T2* mapping and 3D DCE-MRI) with CEUS and PAI. At this intermediate stage, neither placental perfusion nor oxygenation metrics differed between RUPP and controls across modalities, and fetal brain and liver oxygenation measures were likewise comparable. However, exploratory cross-modality analyses revealed coherent correlations between specific CEUS perfusion measures and MRI-derived R2* readouts, suggesting that physiological coupling between perfusion and oxygenation remains detectable within the cohort even when group means are similar. This chapter therefore supports the view that GD16 represents a compensated phase in which detectable between-group differences may be small or heterogeneous, reinforcing the importance of gestational timing, sensitivity, and analytical strategies that capture dispersion and within-litter variability. In Chapter 7, the thesis findings are integrated into a temporally evolving trajectory of placental insufficiency in the RUPP model. Immediately after mechanical reduction of uterine blood flow (GD14), placental function is dominated by an acute ischemic insult with pronounced perfusion impairment. By mid-gestation (around GD16), perfusion and oxygenation measures can appear functionally compensated despite established structural abnormalities at the maternal–fetal interface. By late gestation (GD19), perfusion metrics remain largely preserved, yet placental T2* indicates chronic hypoxia, consistent with a state in which oxygenation is constrained by impaired uteroplacental remodeling rather than by insufficient inflow alone. Overall, this thesis demonstrates that placental insufficiency in the RUPP model is not a static low-perfusion phenotype but a time-dependent sequence in which acute hemodynamic disruption, structural vascular maladaptation, and late oxygenation deficits are only partially aligned in time. These findings argue for time-specific, multimodal imaging biomarker strategies that integrate perfusion and oxygenation readouts and that explicitly address heterogeneity within litters and across placentas. Such temporally informed functional outcomes provide a platform for designing mechanistic studies and for testing therapies. They help align interventions with the window in which the targeted pathophysiology is most detectable and most modifiable.