1. University Hospital Münster , Clinic of Obstetrics and Gynecology , Albert-Schweitzer-Campus 1 , 48149 Münster , Germany , Tel.: 0049-157-89373685, Fax: 0049-251-8347778
2. Institute of Biostatistics and Clinical Research , University of Münster , Münster , Germany
3. University Hospital Münster , Clinic of Obstetrics and Gynecology , Albert-Schweitzer-Campus 1 , 48149 Münster , Germany