1. Department of Gynaecology and Obstetrics, Bronovo Hospital, Bronovolaan 5, 2597 AX The Hague, The Netherlands
2. Department of Obstetrics, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
3. Department of Obstetrics, Leiden University Medical Centre, P.O. Box 9600, 2300 RC Leiden, The Netherlands