1. Department of Obstetrics and Gynecology, University of Bochum, Bochum, Germany; Department of obstetrics and Gynecology, University of Maastricht, Maastricht, The Netherlands
2. Department of Obstetrics and Gynecology, University of Bochum, Bochum, Germany; Department of obstetrics and Gynecology, University of Maastricht, Maastricht, The Netherlands; Universitätsfrauenklinik Bochum, Knappschaftskrankenhaus, In der Schornau 23-25, 44982 Bochum;