1. Department of Obstetrics and Gynaecology; VU University Medical Centre; Amsterdam The Netherlands
2. Department of Epidemiology and Biostatistics; VU University Medical Centre; Amsterdam The Netherlands
3. Department of Obstetrics and Gynaecology; Radboud University Medical Centre; Nijmegen The Netherlands
4. Department of Obstetrics and Gynaecology; Leiden University Medical Centre; Leiden The Netherlands