1. Department of Obstetrics and Gynecology, University of Witten-Herdecke, Community Hospital Dormagen, Dormagen, Germany
2. Department of Obstetrics and Gynecology, University Hospitals Schleswig-Holstein, Kiel, Germany
3. Institute of Anatomy, Christian-Albrechts University Kiel, Kiel, Germany
4. Department of Obstetrics and Gynecology, Community Hospital Dormagen, Dormagen, Germany
5. Department of Anesthesiology, Community Hospital Dormagen, Dormagen, Germany
6. Department of Obstetrics and Gynecology, University Witten-Herdecke, Witten, Germany
7. Department of Obstetrics and Gynecology, Klinikum St. Marien Amberg, Amberg, Germany