1 Division of Obstetric Anesthesiology, Department of Anesthesiology, Vanderbilt University Medical Center, Nashville, Tennessee.
2 Division of Anesthesiology and Critical Care Medicine, Department of Anesthesiology, U.T. Health Science Center San Antonio, San Antonio, Texas.
3 Division of Neuroradiology, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institution, Baltimore, Maryland.
4 Division of Maternal-Fetal Medicine and Surgical Critical Care, Department of Obstetrics and Gynecology and Anesthesiology, University of Texas Medical Branch at Galveston, Galveston, Texas.