1. Leuven University Fertility Centre, Department of Obstetrics & Gynaecology, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium, Tel: +32 1634 3624; Fax: +32 1634 3607;
2. Institute of Primate Research, Division of Reproductive Biology, Karen, Nairobi, Kenya