1. St. Marienkrankenhaus, Richard-Wagner-Straße 14, 60318 Frankfurt am Main, Germany
2. Department of Obstetrics and Gynaecology, Faculty of Medicine, Johann Wolfgang Goethe University Frankfurt am Main, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany
3. Marien-Hospital Witten, Marienplatz 2, 58452 Witten, Germany
4. Institute of Biostatistics and Mathematical Modelling, Johann Wolfgang Goethe University Frankfurt am Main, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany