1 Department of Obstetrics and Gynaecology, Radboud University Medical Centre, PO Box 9101, Nijmegen 6500HB, The Netherlands.
2 Scientific Institute of Quality of Healthcare, Radboud University Medical Centre, PO Box 9101, Nijmegen 6500 HB, The Netherlands.
3 Department of Obstetrics and Gynaecology, University Medical Centre Groningen, University of Groningen, PO Box 30.001, Groningen 9700RB, The Netherlands.
4 The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, 5005 SA Adelaide, Australia.
5 Centre for Reproductive Medicine, Academic Medical Centre, PO Box 22660, 1100DD Amsterdam, The Netherlands.
6 Department of Obstetrics and Gynaecology, Radboud University Medical Centre, PO Box 9101, Nijmegen 6500HB, The Netherlands willianne.nelen@radboudumc.nl.