Symposium: Update on prediction and management of OHSS. Prevention of OHSS: GnRH agonist versus HCG to trigger ovulation.

Ovarian hyperstimulation syndrome (OHSS) remains a major complication of IVF. Triggering ovulation with human chorionic gonadotrophin (RCG) (as a surrogate to LH) is a major factor in the initiation of OHSS. The pathological process usually intensifies if pregnancy is achieved, as the rising endogenous HCG overstimulates the corpora lutea. Decreasing HCG trigger dose does not prevent OHSS. Gonadotrophin-releasing hormone agonists (GnRHa) induce endogenous LH and FSH surges that reliably trigger ovulation, even if a GnRH antagonist is used during ovarian stimulation. Moreover, such a trigger quickly and irreversibly induces luteolysis, thereby preventing OHSS. Contrasting reports regarding clinical outcome probably reflect different approaches to luteal phase support. Zygotes or embryos frozen post GnRHa trigger give excellent clinical outcome post thaw. In summary, GnRHa trigger is the key for complete OHSS prevention.