1. Department of Gynaecology and Obstetrics, Máxima Medical Centre, De Run 4600, 5500 MB Veldhoven, The Netherlands
2. Department of Gynaecology and Obstetrics, Isala Klinieken, Dokter van Heesweg 2, 8025 AB Zwolle, The Netherlands
3. Department of Gynaecology and Obstetrics, Zorggroep Twente, Zilvermeeuw 1, 7609 PP Almelo, The Netherlands
4. Department of Epidemiology, CAPHRI Research School, Maastricht University, Minderbroedersberg 4-6, 6211 LK Maastrich, The Netherlands
5. Department of Gynaecology and Obstetrics, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands