Ovarian Hyperstimulation Syndrome after GnRH Agonist Triggering and Freeze-All Protocol? Never Not, Hardly Ever: A Systematic Review of Case Reports

Introduction: Ovarian hyperstimulation syndrome (OHSS) is a severe complication associated with controlled ovarian stimulation (COS). GnRH agonist (GnRH-a) triggering is considered an efficient strategy to prevent OHSS in the high-risk patient. Methods: We performed a review of 11 cases of early and severe OHSS following GnRH-a triggering and freeze-all protocol. Electronic databases were searched from inception of each database until October 2021, to identify case reports and case series that reported OHSS after GnRH-a triggering and freeze-all approach describing patient demographics, COS protocol, and patient outcomes. Results: From the literature review, it is possible to suggest that (1) following GnRH-a triggering, the risk of early and severe OHSS is not totally cancelled; (2) despite it is not possible to predict the event, polycystic ovary syndrome is the most common risk factor; (3) the use of GnRH antagonist starting from the day of PU may represent a valid strategy for preventing OHSS in women with high-risk profile; (4) following the unexpected onset of OHSS, measuring serum levels of human chorionic gonadotropin (hCG) is helpful to exclude an inadvertent exogenous administration or a pregnancy. Conclusion: The statement that OHSS risk is eliminated when GnRH-a triggering, a freeze-all strategy, and no hCG in the luteal phase may generate the idea that this event cannot occur. Although rare, these cases have been observed in a relatively short period of time.