Ovarian hyperstimulation syndrome is an iatrogenic complication of controlled ovarian stimulation. Ovarian hyperstimulation syndrome prevention is a multistage process and more important than treatment.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.