1. Department of Obstetrics and Gynaecology, Vrije Universiteit Medical
Center, 1081 HV Amsterdam, The Netherlands
2. Department of Obstetrics and Gynaecology, Medisch Spectrum Twente,
7511 JX Enschede, The Netherlands
3. Department of Clinical Chemistry, Vrije Universiteit Medical Center,
1081 HV Amsterdam, The Netherlands