1. Department of Obstetrics & Gynecology, University of Washington, P.O. Box 359865, Seattle, WA 98104, USA
2. American College of Obstetricians and Gynecologists, Department of Research, 409 12th Street SW, Washington, DC 20024, USA
3. Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Wayne State University School of Medicine, 3990 John R Street, 7 Brush North, P.O. Box 163, Detroit, MI 48201, USA