Survival rate of human oocytes and pregnancy outcome after vitrification using slush nitrogen in assisted reproductive technologies

ObjectiveTo report the survival rate of oocytes and the rate of successful pregnancies obtained from super-rapid cooling of oocytes using slush nitrogen (SN2).DesignProspective clinical research.SettingA university-affiliated hospital.Patient(s)Twenty-eight infertile women who underwent 30 cycles of IVF-ET using previously vitrified oocytes.Intervention(s)Oocytes were vitrified by super-rapid cooling using SN2.Main Outcome Measure(s)Morphological normality of thawed oocytes and clinical outcome.Result(s)In 30 cycles of ovarian stimulation for IVF, 364 surplus oocytes from 28 patients were vitrified using SN2. Three hundred two (85.1% ± 2.9%) of the oocytes survived after warming. Fertilization and cleavage rates were 77.4% ± 3.5% (168/218) and 94.3% ± 2.1% (158/168), respectively. Thirteen pregnancies (43.3%) resulted from 30 uterine transfers of 120 embryos with an implantation rate of 14.2% (17/120). There were no differences between the pregnancy rate after vitrification/warming and that obtained from routine noncryopreserved oocytes.Conclusion(s)The present report suggests that super-rapid cooling may improve the clinical efficacy of human oocyte vitrification and may be a valuable tool for human assisted reproductive technologies.