1. Department of General Practice and Elderly Care Medicine University of Groningen University Medical Centre Groningen Groningen The Netherlands
2. Department of General Practice University of Maastricht Maastricht University Medical Centre Maastricht The Netherlands
3. Department of Obstetrics and Gynaecology Máxima Medical Centre Veldhoven The Netherlands
4. Department of Epidemiology University of Groningen University Medical Centre Groningen Groningen The Netherlands
5. Department of Obstetrics and Gynaecology Grow Research School for Oncology and Developmental Biology University of Maastricht Maastricht The Netherlands