1. Fertility Laboratory, Department of Obstetrics and Gynaecology, Radboud University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands
2. Department of Clinical Chemistry, Maasstad Hospital Rotterdam, PO Box 9100, 3007 AC Rotterdam, The Netherlands
3. Department of Clinical Chemistry, Atalmedial, Medical Diagnostic Centre, PO Box 69641, 1060 CR Amsterdam, The Netherlands
4. Department of Obstetrics and Gynaecology, Radboud University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands