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Background: The efficiency of in vitro maturation (IVM) techniques is suboptimal compared with controlled ovarian stimulation combined with IVF cycles, and studies are needed to identify factors that predispose IVM cycles to success or failure. We compared the outcome of IVM cycles with different dominant follicle (DF) size at oocyte retrieval following hCG priming., Methods: IVM was performed in 160 patients with polycystic ovaries (171 cycles). We administered 10,000 IU hCG s.c. 35-38 h before oocyte collection when endometrial thickness reached at least 6 mm. IVM cycles were retrospectively analyzed according to DF diameter as follows; Group 1: DF diameter 14 mm. RESULTS A positive correlation was observed between DF size and number of in vivo matured oocytes collected (Group 1, 2 and 3 = 6.9, 10.6 and 15.1%, respectively). The rates of IVM, fertilization and embryo development were similar among the sibling immature oocytes collected from the three groups. However, clinical pregnancy rate in Group 2 (40.3%) was higher than Group 3 (17.1%) (P < 0.05). Moreover, implantation rates in Groups 1 (13.6%) and 2 (14.3%) were higher than Group 3 (4.9%) (P < 0.01)., Conclusions: Our results suggest that oocyte collection in IVM cycles should be performed when the DF is 14 mm diameter or less. Sibling immature oocytes may be affected detrimentally if a DF >14 mm is present at oocyte collection.

Background: Our aim was to evaluate whether extending the interval between human chorionic gonadotrophin (hCG) priming and immature oocyte retrieval increases the oocyte maturation rate following in vitro maturation (IVM)., Methods: This study was performed retrospectively. IVM was performed on 113 polycystic ovary syndrome patients (n = 120 cycles). Oocyte collection was performed either 35 h (Group 1; n = 76) or 38 h (Group 2; n = 44) after 10,000 IU of hCG priming. Following oocyte retrieval, oocyte maturity was assessed and the remaining immature oocytes were cultured in IVM medium up to Day 2., Results: The number of in vivo matured oocytes collected was significantly higher in Group 2 (13.6%, 114/840 versus 7.3%, 96/1312 in Group 1) (P < 0.01); the oocyte maturation rate after Day 1 was significantly higher (P < 0.01) in Group 2 (46.3 versus 36.0% in Group 1); and clinical pregnancy (40.9 versus 25%) and implantation rates (15.6 versus 9.6%) were better in Group 2 than those in Group 1., Conclusions: The results suggest that extending the period of hCG priming time from 35 to 38 h for immature oocyte retrieval promotes oocyte maturation in vivo and increases the IVM rate of immature oocytes. Therefore, oocyte retrieval after 38 h of hCG priming may improve subsequent pregnancy outcome in cycles programmed for IVM treatment.