Objective: To examine whether the presence of birefringent spindles in living human oocytes can be used as a predictive factor associated with embryo morphology to allow embryo selection before transfer and its association with IVF outcomes. Design: Prospective study. Setting: Assisted reproduction center in Brazil. Patient(s): One hundred fifty-seven patients undergoing intracytoplasmic sperm injection cycles, resulting in 1,097 metaphase II oocytes. Intervention(s): Meiotic spindles were evaluated before intracytoplasmic sperm injection in all metaphase II oocytes. Main Outcome Measure(s): Meiotic spindles' imaging and fertilization rate, embryo development, and implantation rate. Result(s): Birefringent spindles were detected in 65.9% (SD group). The normal fertilization rate and rate of early-cleavaged embryos were higher in the SD group compared with in the spindle-non-detected (SND) group. When only embryos from the SD group were selected for transfer, the pregnancy and implantation rates were 44.4% and 23.0%, and when only embryos from the SND group were transferred, those rates were 18.2% and 8.7%, respectively (statistically significant differences). Conclusion(s): Spindle visualization can be an important tool for predicting better fertilization potential, embryo development, and clinical outcomes, suggesting that embryo selection for transfer may be based not only on embryo morphology but also on oocyte nuclear maturity. © 2008 American Society for Reproductive Medicine.
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