Ovarian stimulation, oocyte retrieval and embryo culture Controlled ovarian hyperstimulation was carried out in an antagonist protocol using recombinant FSH combined with a GnRH antagonist (ganirelix, Orgalutran, NV Organon) (Kolibianakis et al., 2004) or an agonist protocol, using GnRH analogues for pituitary desensitisation (buserilin, Suprefact; Hoechst, Frankfurt, Germany), combined with human menopausal gonadotrophins (hMG)(Menopur, Ferring Pharmaceuticals A/S, Copenhagen, Denmark) or recombinant FSH (Puregon, NV Organon, Oss, The Netherlands)(Van de Velde et al., 1998). Final oocyte maturation was induced by the administration of 10,000 IU of HCG. Transvaginal ultrasound-guided oocyte retrieval was scheduled 36 h after HCG administration. ICSI was used to fertilize the oocytes. Sperm preparation, in vitro fertilization, intracytoplasmic sperm injection procedures and embryo culture were carried out as described by Van Landuyt et al. (2005).