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This study compared the embryological characteristics and clinical outcome of in-vitro maturation (IVM) treatment cycles with and without in-vivo matured oocytes collected following human chorionic gonadotrophin (HCG) priming. The patients were administered 10,000 IU of HCG subcutaneously when endometrial thickness reached > or =6 mm and oocyte collection was performed 35-36 h after HCG administration. The clinical outcome and embryological aspects were analysed between IVM cycles with (group 1) and without (group 2) in-vivo matured oocytes. In group 1, three (range 1-12) in-vivo matured oocytes per patient were retrieved on average. The number of good quality embryos derived from in-vivo matured oocytes in group 1 was significantly higher than those derived from in-vitro matured oocytes in group 1 and group 2 (P < 0.05). However, there was no difference between the number of good quality embryos produced from in-vitro matured oocytes in the two groups. There were 12 clinical pregnancies (40.0%) in group 1, and seven pregnancies (23.3%) in group 2. These results suggest that IVM cycles with in-vivo matured oocytes resulted in a good clinical pregnancy rate, which could be explained by the superior quality of embryos derived from the in-vivo matured oocytes.

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.