1. Department of Obstetrics and Gynecology; Cantonal Hospital Frauenfeld; Switzerland
2. Department of Obstetrics and Gynecology; Georg August University Goettingen; Germany
3. Department of Obstetrics and Gynecology; Lutheran Hospital Hagen-Haspe; Germany
4. Department of Obstetrics and Gynecology; Medical University of Lodz; Lodz Poland
5. Institute of Medical Statistics; Georg August University; Goettingen Germany