1. Department of Obstetrics and Gynecology, The George Washington University, 2150 Pennsylvania Avenue, Washington DC 20037, NW, USA
2. Department of Obstetrics and Gynecology, University of Kentucky School of Medicine, Lexington, KY, USA
3. Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, NC, USA
4. Frauenklinik Erfurt, Erfurt, Germany