Abstract: Objective To evaluate the effects of gonadotropic releasing hormone antagonist (GnRH-ant) on the prevention of early ovarian hyperstimulation syndrome (OHSS). MethodsA total of 174 patients with high risk of OHSS were enrolled based on the following criteria: on HCG day ≥25 follicles with a diameter> 14 mm or ≥20 oocytes and ≥5 000 pg/ml serum E2 concentration. All the patients were subject to embryo freezing and scheduled transplantation in addition to routine expansion for OHSS prevention. The GnRH-ant group (n=87) was subcutaneously injected with 0.25 mg GnRH-ant on Day 1 after egg retrieval for five consecutive days. Patients in the control group was given routine therapy (n=87). The levels of serum vascular endothelial growth factor (VEGF) were measured on Days 0, 2, 4 and 6. ResultsThe treatment group produced remarkably lower levels of VEGF on Days 4 and 6, compared with the control group (P<0.05). Meanwhile, compared with the control, on Day 6 the treatment group showed marked decreases in hematocrit and ascite (P<0.05), hospitalization stay (P<0.01), and the incidence of moderate to severe OHSS (3.4%) (P<0.05). ConclusionsAdministration of GnRH-ant on the day of oocyte collection has certain preventive effects on early OHSS, which can reduce ascites and hematocrit, relieve symptoms, and reduce the level of VEGF level, but its mechanism remains to be studied. GnRH-ant is simple and safe to be used as a preventive approach for high-risk OHSS patients.