Ovarian hyperstimulation syndrome is an iatrogenic complication of controlled ovarian stimulation. Early ovarian hyperstimulation syndrome (OHSS) occurs during luteal phase of controlled ovarian stimulation within 9 days after human chorionic gonadotropin trigger and reflects an acute consequence of this hormone on the ovaries.Ovarian hyperstimulation syndrome prevention is a multistage process and more important than treatment.Recently the administration of GnRH antagonists during the luteal phase of in vitro fertilization cycles offers another therapeutic modality for patients with severe early OHSS.However, preventive administration of GnRH antagonist for high risk OHSS patients from the day of oocyte retrieval is not investigated. Besides, the relevant mechanism is not clear yet. Here we designed a prospective randomized study to investigate whether GnRH anatagonist treatment after oocyte retrieval is more effective in preventing early ovarian hyperstimulation syndrome development than traditional aspirin preventive administration in women at high risk for OHSS.