Multinational, multicentre, open label, randomized, 2-arm parallel-group phase IV study. Eligible patients will be randomly allocated to one of the two groups: the agonist group will receive Decapeptyl® 0.1 mg (triptorelin) starting in the mid-luteal phase of the natural cycle until downregulation until the day of ovulation induction. The antagonist group will receive cetrorelix 0.25 mg from stimulation day 6 to ovulation induction. In both groups, Pergoveris® 150 I.U./75 I.U. (r-hFSH/r-hLH) will be used for ovarian stimulation from cycle day 2 to ovulation induction.