1. Pain Center, Department of Anaesthesiology, University Medical Center Groningen (UMCG), University of Groningen, 9713 GZ Groningen, The Netherlands
2. Department of Rehabilitation Medicine, University Medical Center Groningen (UMCG), University of Groningen, 9713 GZ Groningen, The Netherlands
3. Department of Obstetrics and Gynaecology, University Medical Center Groningen (UMCG), University of Groningen, 9713 GZ Groningen, The Netherlands