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

Objective: To report the survival rate of oocytes and the rate of successful pregnancies obtained from super-rapid cooling of oocytes using slush nitrogen (SN(2)).
Design: Prospective clinical research.
Setting: A 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 SN(2).
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 SN(2). 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.