1. Department of Obstetrics and Gynecology , Vivantes Klinikum im Friedrichshain, Affiliate of Charité University , Berlin , Germany
2. Institute of Medical Statistics , Berlin , Germany
3. Department of Obstetrics and Gynecology , Sana Klinikum Lichtenberg , Berlin , Germany
4. Department of Obstetrics and Gynecology , University of Aachen , Aachen , Germany