Preeclampsia is a life-threatening pregnancy disorder that occurs when the placenta microvasculature fails to develop properly. Ultrasound imaging is the ubiquitous tool for pregnancy imaging, but current clinical imaging systems lack sufficient resolution and contrast to assess the microstructure of the placenta. Quantitative ultrasound (QUS) analyzes the raw radiofrequency (RF) information from ultrasound image acquisitions to estimate the size, concentration, and organization of ultrasound scatterers that make up the tissue microstructure. Our goal is to apply QUS to detect changes in placental microstructure in vivo using an established rat model of preeclampsia. Rat placentas are comprised of two major regions: the junctional zone, where the maternal microvasculature delivers nutrient rich blood to the placenta, and the labyrinth zone, where the maternal blood delivers nutrients to the fetal blood supply. Using QUS, we can distinguish between the junctional zone and labyrinth zone by estimating the Effective Scatterer Diameter (ESD) throughout the placenta. Preeclamptic rats have smaller, underdeveloped junctional zone compared to normal rats, and this can be seen in histology (ex vivo). We can also measure this difference between normal and preeclamptic placentas in vivo using the ESD maps generated using QUS techniques. This pre-clinical study demonstrates that QUS shows promise as a tool to monitor placental health in human cases of preeclampsia.