1. Department of Obstetrics and Gynecology, Duke University, Durham, North Carolina
2. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of North Carolina, Chapel Hill, North Carolina
3. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Duke University, Durham, North Carolina
4. Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah