• OHSS occurrence assessed one week after oocyte retrieval
  
• Implantation rate assessed at seven weeks gestation
  

• Clinical Pregnancy rate assessed at time of ultrasound
  
• Mature oocytes assessed at time of retrieval
  
• Ovarian volume assessed one week after oocyte retrieval
  

OHSS is an iatrogenic complication of controlled ovarian hyperstimulation, which in its severe form, may result in significant morbidity. Although, there have been significant advances in in-vitro fertilization (IVF) protocols over the years, the incidence of OHSS have remained stable and there is currently no effective way of preventing this disorder.

hCG is commonly used as a substitute for the endogenous LH surge to induce final oocyte maturation in IVF. Unfortunately, hCG results in a prolonged luteotropic effect because of its long half-life which may result in a potential risk of OHSS in high-risk patients. In contrast, induction of endogenous LH surge with a GnRH agonist may result in a reduced risk of OHSS. This is due both to the shorter half-life of the endogenous LH surge and the subsequent pituitary suppression leading to early luteolysis. However, previous studies have suggested that this approach may impair implantation rates.

There are no randomized studies assessing the effect of GnRH agonist to induce oocyte maturation on the occurrence of OHSS and implantation rates in high-risk patients. The aims of this study are to compare the incidence of OHSS and implantation rates among high-risk patients who used either GnRH agonist or hCG to trigger oocyte maturation after prevention of premature LH surge with either a GnRH antagonist protocol or the dual pituitary suppression protocol, respectively.

High risk patients include women with polycystic ovarian syndrome (PCOS) or PCO morphology (PCOM) on ultrasound without the clinical or biochemical evidence of the syndrome, and patients with previous high response to gonadotropins.