To test this hypothesis, our interdisciplinary research team at UCLA will first develop non-contrast freebreathing placental mp-MRI, consisting of multi-delay pseudo-continuous arterial spin labeling (pCASL) perfusion and high-resolution multi-contrast structural MRI, which will provide reproducible measures of placental perfusion and tissue microstructure (AIM 1). The novel mp-MRI techniques will be compared to the uterine artery Doppler ultrasound through pregnancy and validated ultimately by the gold standard histological pathology and vascularity of the post-parturient placenta (AIM 2). Lastly, the investigators will perform in-depth analyses of recruited subjects for exposure to environmental pollution and correlate their rates of exposure to extensively collected pregnancy outcomes, towards building a predictive model (AIM 3). Our specific aims are: