Background: A bolus dose of GnRH agonist can substitute for hCG as a trigger for the resumption of meiosis in ovarian stimulation with GnRH antagonists, which has been suggested to reduce the risk of ovarian hyperstimulation syndrome (OHSS). As the efficacy of this measure in fresh embryo transfer (ET) cycles is unclear, we evaluated a new clinical concept of GnRH-agonist triggering. Methods: In this prospective, observational proof-of-concept study, 20 patients considered at increased risk of developing OHSS (≥20 follicles ≥10 mm or estradiol ≥4000 pg/ml, or a history of cycle cancellation due to OHSS risk or the development of severe OHSS in a previous cycle) after ovarian stimulation and concomitant GnRH-antagonist administration had final oocyte maturation triggered with 0.2 mg triptorelin s.c. All two pronucleate (2 PN) oocytes were cryopreserved by vitrification, and frozen-thawed ETs (FT-ETs) were performed in an artificial cycle. Main outcome measures were the cumulative ongoing pregnancy rate per patient and the ongoing pregnancy rate per first ET. Secondary outcomes included the incidence of moderate-to-severe OHSS. Results: Of the 20 patients triggered with GnRH agonist, 19 patients underwent 24 FT-ETs in the observational period. The cumulative ongoing pregnancy rate was 36.8% (95% confidence interval: 19.1-59.0%). The ongoing pregnancy rate per first FT-ET was 31.6% (15.4-54.0%). No cases of moderate or severe OHSS were observed. Conclusions: The present study is the proof of the concept that GnRH-agonist triggering of final oocyte maturation in combination with elective cryopreservation of 2 PN oocytes offers OHSS risk patients a good chance of pregnancy achievement, while reducing the risk of moderate and severe OHSS.