1. Department of Obstetrics and Gynaecology; Academic Medical Centre; University of Amsterdam; Amsterdam the Netherlands
2. Department of Clinical Epidemiology, Biostatistics and Bioinformatics; Academic Medical Centre; University of Amsterdam; Amsterdam the Netherlands
3. Division of Maternal Fetal Medicine; Department of Obstetrics and Gynecology; Thomas Jefferson University; Philadelphia PA USA
4. Depertment of Obstetrics and Gynaecology; OLVG Oost; Amsterdam the Netherlands
5. Medical Library; Academic Medical Centre; Amsterdam the Netherlands
6. Department of Obstetrics and Gynaecology; Noordwest Ziekenhuisgroep; Alkmaar the Netherlands