1. Department of Obstetrics and Gynaecology, Radboud University Medical Centre, Nijmegen, the Netherlands
2. Department of Obstetrics and Gynaecology, Canisius Wilhelmina Hospital, Nijmegen, the Netherlands
3. Faculty of Medical Sciences, University Medical Centre Groningen, Groningen, the Netherlands
4. Department of Obstetrics and Gynaecology, Helios Klinikum Duisburg, Duisburg, Germany
5. Department of Obstetrics and Gynaecology, Maxima Medical Centre, Veldhoven, the Netherlands