1. Department of Obstetrics and Gynaecology; Martini Hospital; Groningen The Netherlands
2. Department of Obstetrics and Gynaecology; Deventer Hospital; Deventer The Netherlands
3. Department of Obstetrics and Gynaecology; Academic Medical Centre; University of Amsterdam; Amsterdam The Netherlands
4. Department of Gynaecology and Reproductive Medicine; University Medical Centre Utrecht; Utrecht The Netherlands