1. Obstetrics and Gynecology Department, Centre Hospitalier Universitaire de Liège, Citadelle Hospital, Boulevard du 12ème de Ligne 1, 4000 Liege, Belgium
2. Center for Reproductive Medicine, University of Liège, Citadelle Hospital, Boulevard du 12ème de Ligne 1, 4000 Liege, Belgium
3. Department of Statistical Analysis, University of Liège (ULiège), 4000 Liege, Belgium