1. Department of Obstetrics and Prenatal Medicine, University Hospital Bonn, 53127 Bonn, Germany
2. Pränatal-Medizin München, 80639 Munich, Germany
3. Department of Prenatal Medicine, St. Josef Hospital, 93053 Regensburg, Germany
4. Division of Prenatal Medicine and Gynecologic Sonography, Department of Obstetrics and Gynecology, University of Cologne, 50931 Cologne, Germany