OBJECTIVE: To investigate the kinetics of serum vascular endothelial growth factor (VEGF) following gonadotrophin-releasing hormone (GnRH) antagonist administration in the luteal phase in women with established severe early ovarian hyperstimulation syndrome (OHSS).DESIGN: Pilot observational cohort study.SETTING: Private in vitro fertilisation (IVF) Unit.POPULATION: Twelve IVF women diagnosed with established severe early OHSS 5 days post oocyte retrieval (POR).METHODS: Women undergoing IVF diagnosed with severe early OHSS 5 days POR were given 0.25 mg GnRH antagonist for 4 days, from day 5 until and including day 8 POR, combined with elective blastocyst cryopreservation. Serum VEGF was measured from the day of oocyte retrieval until day 11 POR. Ovarian volume, ascites, serum estradiol and progesterone, haematocrit and white blood cells were monitored during the same period.MAIN OUTCOME MEASURES: Kinetics of VEGF following luteal GnRH antagonist administration in women with established severe early OHSS.RESULTS: The concentration of VEGF was highest (390.9 ± 137.4 pg/ml) 5 days POR, coinciding with the day of diagnosis of severe OHSS. There was a significant decline of VEGF on day 7 (302.8 ± 104.9 pg/ml; P = 0.026), day 9 (303.3 ± 148.3 pg/ml; P = 0.007), and day 11 (252.6 ± 182.7 pg/ml; P = 0.010) compared with day 5 POR. This decline was associated with an improvement of ultrasound and laboratory parameters, indicating regression of severe OHSS. All women were managed at an outpatient level.CONCLUSIONS: GnRH antagonist administration in the luteal phase is associated with a significant decline of VEGF and with regression of established severe early OHSS.