For all subjects, a fixed dose of gonadotropin-releasing hormone (GnRH) antagonist will be injected daily as soon as one of the follicles reaches the ≥14 mm diameter and stopped one day before oocyte pick up (OPU); ovulatory dose of human chorionic gonadotropin (hCG) could be administered when at least one follicle reaches 16.5 mm in diameter.