1. From the Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine (K.R.U., B.H.G., R.H.C.), and Department of Radiology (A.E.P., E.G.G., D.K.W.), Keck School of Medicine, University of Southern California, 2020 Zonal Ave, IRD 203, Los Angeles, CA 90033.