1. Department of Obstetrics and Gynaecology; Erlangen University Hospital; Erlangen Germany
2. Department of Obstetrics and Gynaecology; University Medical Centre Mannheim, Heidelberg University; Heidelberg Germany
3. Department of Obstetrics; Charité Virchow-Klinikum; Berlin Germany
4. Department of Obstetrics and Gynaecology; University Medical Centre Mainz; Mainz Germany
5. Department of Medical Statistics and Biomathematics; University Medical Centre Mannheim, Heidelberg University; Heidelberg Germany