STUDY QUESTIONAre clinical pregnancy rates satisfactory and the incidence of OHSS low after GnRH agonist trigger and modified intensive luteal support in patients with a high risk of ovarian hyperstimulation syndrome (OHSS)?SUMMARY ANSWERGnRH agonist trigger combined with 1500 IU hCG at the time of oocyte retrieval and subsequent estradiol and progesterone replacement in OHSS high-risk patients can facilitate fresh embryo transfer with high clinical pregnancy rates and a low risk of severe OHSS.WHAT IS KNOWN ALREADYConventional luteal support packages are inadequate to facilitate a fresh transfer after a GnRH agonist trigger. A low dose of hCG (1500 IU) after oocyte aspiration can be used to replace the actions of early luteal LH to sustain implantation and the function of the early corpus luteum, although the level of risk of severe OHSS with this strategy is unclear.STUDY DESIGN, SIZE, DURATIONThis international multicentre retrospective case study, including 275 women at high risk of OHSS, was undertaken during the period January 2011-December 2012.PARTICIPANTS/ MATERIALS, SETTING, METHODSWomen were identified as at high risk of OHSS, based on IVF response, ovarian reserve characteristics and previous history of having had treatment, in three clinical IVF centres in UK, Belgium and Australia. All three centres used a GnRH agonist trigger followed by one bolus of 1500 IU hCG 1h after oocyte retrieval. Moreover, the luteal phase was supported with daily vaginal progesterone and twice daily estradiol valerate.MAIN RESULTS AND THE ROLE OF CHANCEA total of 275 autologous cycles with fresh transfer were undertaken in a cohort of high-risk women as defined by baseline characteristics [median (interquartile range)]: age 31.6 (29-35) years, antral follicle count median 25 (18-34) and anti-Müllerian hormone median 49.1 pmol/l (35.2-69.3). At the end of stimulation, the peak estradiol median of 12 000 pmol/l (9400-15 914) and the mean oocyte yield of 17.8 ± 8.4 confirmed a high response. The overall clinical pregnancy rate was 41.8% per cycle started, with only two cases of severe OHSS reported (0.72%). No significant differences in clinical pregnancy rates between centres were identified.LIMITATIONS, REASONS FOR CAUTIONThis is a retrospective study and future randomized controlled trials will be able to compare whether these outcomes can be improved upon by either segmentation of the stimulation cycle and embryo transfer or alternative aggressive luteal support strategies.WIDER IMPLICATIONS OF THE FINDINGSIn women who are undergoing ovarian stimulation and who develop an excessive ovarian response, the use of a GnRH agonist trigger combined with modified luteal support can provide the opportunity to proceed to fresh embryo transfer with adequate clinical pregnancy rates. However, this procedure will not completely eliminate the risk of OHSS and for women with an extreme ovarian response or with significant comorbidity, where the possibility of severe OHSS is unacceptable, we recommend GnRH agonist trigger followed by a freeze-all policy to completely avoid OHSS.