The purpose of this study is to compare pregnancy rates and the occurrence of OHSS in PCOS patients who were treated with GnRH agonist and GnRH antagonist protocols ovarian stimulation during an IVF cycle. Our hypothesis is that the GnRH antagonist protocol reduces the occurrence and severity of OHSS compared to the GnRH agonist protocol.

Women with polycystic ovarian syndrome (PCOS) represent a group of patients at high risk of developing ovarian hyperstimulation syndrome (OHSS), an iatrogenic complication of ovarian stimulation during IVF treatment. In contrast to mild OHSS, severe OHSS is a life-threatening complication, characterized by massive ovarian enlargement, ascites, pleural effusion, oliguria, haemoconcentration and thromboembolic phenomena. Currently, no curative therapy for OHSS is available and thus prevention is considered the most effective "treatment". Several measures have been adopted to reduce the occurrence of the syndrome, the most effective being cycle cancellation and withholding of human chorionic gonadotropin (hCG), which seems to be the most critical factor for the development of OHSS.

COMPARISON: This study aims to compare the development and severity of OHSS, as well as ongoing pregnancy rates in PCOS patients who received a flexible GnRH antagonist (Ganirelix) protocol vs a long GnRH agonist (Arvekap) protocol of ovarian stimulation.

Inclusion Criteria:

• Clinical diagnosis of PCOS (presence of oligo-ovulation/anovulation and polycystic ovaries)

Exclusion Criteria:

• Normal responders
• Poor responders