1. Fetal Medicine Unit, University Medical Centre Groningen; University of Groningen; 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. Department of Obstetrics and Gynaecology; University of Tübingen; Tübingen Germany