1. Department of Obstetrics and Gynecology, University Hospital, University of Duisburg-Essen, 45147 Essen, Germany
2. Department of Pediatrics, University Hospital Essen, University of Duisburg-Essen, 45147 Essen, Germany
3. Institute for Medical Informatics, Biometry and Epidemiology, University of Duisburg-Essen, 45147 Essen, Germany
4. Department of Obstetrics and Gynecology, University Hospital of Lübeck, 23562 Lübeck, Germany
5. Department of Obstetrics and Gynecology, University Hospital of Kiel, 24105 Kiel, Germany
6. Department of Obstetrics and Gynecology, University Hospital of Würzburg, 97080 Würzburg, Germany
7. Department of Obstetrics, Jena University Hospital, 07747 Jena, Germany