1. Fetal Medicine Unit, Department of Obstetrics and Gynaecology; University Medical Centre Groningen; The Netherlands
2. Department of Obstetrics and Gynecology; St Antonius Hospital; Nieuwegein The Netherlands
3. Department of Statistics; St Antonius Hospital; Nieuwegein The Netherlands
4. Fetal Medicine Unit, Department of Obstetrics and Gynaecology; Academic Medical Centre; Amsterdam The Netherlands
5. Department of Obstetrics and Gynaecology; University of Tuebingen; Tuebingen Germany