The aim of this retrospective study was to evaluate the effectiveness of gonadotrophin-releasing hormone agonist (GnRHa) to trigger oocyte maturation in patients with polycystic ovarian syndrome (PCOS) or previous high response. The outcome of ovarian stimulation and IVF in patients using GnRHa to trigger oocyte maturation after co-treatment with GnRH antagonist (study group) was compared with patients using human chorionic gonadotrophin (HCG) to trigger oocyte maturation after a dual pituitary suppression protocol with oral contraceptive pill (OCP) and GnRHa overlap (control group). All patients received intramuscular progesterone for luteal support but patients in the study group received additional supplementation with oestradiol patches. The mean number of oocytes, proportion of mature oocytes and fertilization rate were similar between the study and control groups. Implantation rate (38.6% versus 45.1%), clinical pregnancy rate (69.6% versus 60.9%) and delivery rate (62.5% versus 56.5%) were similar in the study and control groups respectively. There was one case of moderate ovarian hyperstimulation syndrome (OHSS) in the control group and none in the study group. GnRHa is effective in triggering oocyte maturation in patients with PCOS or previous high response. Further randomized studies are required to evaluate its effectiveness in the prevention of OHSS in this group of patients.