1 Department of Obstetrics and Gynaecology, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands a.m.van.oers@umcg.nl.
2 Department of Epidemiology, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands.
3 Department of Obstetrics and Gynaecology, University of Groningen, University Medical Center Groningen, 9700RB Groningen, The Netherlands.
4 Department of General Practice, University of Utrecht, University Medical Center Utrecht, 3508GA Utrecht, The Netherlands.
5 Department of Obstetrics and Gynaecology, Scheper Hospital, Department of Obstetrics and Gynaecology, 7800RA Emmen, The Netherlands.
6 Department of Obstetrics and Gynaecology, Isala Clinics, 8000GK Zwolle, The Netherlands.
7 Department of Obstetrics and Gynaecology, Medical Center Leeuwarden, 8901BR Leeuwarden, The Netherlands.
8 Department of Obstetrics and Gynaecology, Maxima Medical Center, 5500MB Veldhoven, The Netherlands.
9 Department of Obstetrics and Gynaecology, University of Maastricht, Maastricht University Medical Center, 6202AZ Maastricht, The Netherlands.
10 Department of Obstetrics and Gynaecology, OLVG, 1090HM Amsterdam, The Netherlands.
11 Department of Obstetrics and Gynaecology, Deventer Hospital, 7400GC Deventer, The Netherlands.
12 Department of Obstetrics and Gynaecology, St. Antonius Hospital, 3430EM Nieuwegein, The Netherlands.
13 Department for Reproductive Medicine, Division Female and Baby, University of Utrecht, University Medical Center Utrecht, 3508GA Utrecht, The Netherlands.
14 Department of Obstetrics and Gynaecology, Martini Hospital, 9700RM Groningen, The Netherlands.
15 The Robinson Research Institute, School of Pediatrics and Reproductive Health, University of Adelaide, 5000SA Adelaide, Australia.