Fertilization, embryo development, and clinical outcome of immature oocytes from stimulated intracytoplasmic sperm injection cycles

Objective: To evaluate the fertilization and developmental potential of immature oocytes obtained from controlled ovarian hyperstimulated cycles of patients undergoing intracytoplasmic sperm injection (ICSI). Design: Retrospective study. Setting: Academic assisted reproductive technology program. Patient(s): Two hundred patients with at least one mature oocyte and one immature oocyte (study 1), and 44 patients with no mature oocytes (study 2) at time of oocyte denudation. Intervention(s): Oocyte denudation was per-formed immediately after retrieval. Oocytes were cultured in vitro for 4-6 hours before ICSI and then categorized into four groups: group I, metaphase II (MH) oocytes at denudation; group II, in vitro matured MII oocytes; group III, metaphase I (MI) oocytes that did not progress to MIL, and group 4, germinal-vesicle (GV) oocytes that converted to MI. Main Outcome Measure(s): Fertilization and embryo development were compared among groups in study 1. Pregnancy and implantation rates were evaluated in study 2. Result(S): Although the fertilization rate in group III was significantly lower than in groups I and II, no significant difference was found between groups I and II. Day 3 embryos in group I had the highest mean number of blastomeres, proportions of good embryos, and blastocyst formation rate when compared with groups II and III. Two clinical pregnancies were achieved from 26 transfer cycles in study 2, resulting in pregnancy and implantation rates of 7.7% and 4% per transfer cycle, respectively. Conclusion(S): Although our results show that immature oocytes from stimulated cycles can be normally fertilized and used to increase the number of embryos available for transfer, the increase in number of embryos derived from immature oocytes cannot be efficiently translated into pregnancies and live births. The clinical significance of using immature oocytes in stimulated cycles needs further investigation.