Background: Elevated estradiol (E2) levels and multiple folliculogenesis predispose to development of ovarian hyperstimulation syndrome (OHSS). In patients with GnRH agonist protocol, both withdrawing GnRH agonist and GnRH antagonist administration are associated with a reduction in (E2) levels with subsequent decreasing the incidence and severity of OHSS. This work is to compare the clinical and endocrine outcome response of cycles in which GnRH agonist withdrawing with cycles in which the GnRH antagonist administration in patients at risk of severe OHSS.