Outcome of Cryotransfer of Embryos Developed from Vitrified Oocytes: Double Vitrification Has No Impact on Delivery Rates

Objective: Evaluate the outcome of cryotransfer of embryos developed from vitrified oocytes.

Design: Retrospective cohort study.

Setting: Private university-affiliated IVF center.

Patient(s): Women undergoing warming cycles in which vitrified embryos were developed from vitrified or fresh oocytes.

Intervention(s): Vitrification by the Cryotop open device.

Main Outcome Measure(s): Delivery rate (DR) per warming cycle.

Result(s): A total of 471 warming cycles of 796 vitrified embryos developed from vitrified oocytes (group 1) and 2,629 warming cycles of 4,394 vitrified embryos derived from fresh oocytes (group 2) were evaluated. Overall survival rates were 97.2% [95% confidence interval [CI] 95.9%-98.6%] vs. 95.7% [95% CI 94.9-96.4], respectively. DRs per warming cycle were 33.8% (group 1) and 30.9% (group 2). Double vitrification had no effect on DR (odds ratio [OR] 0.877, 95% CI 0.712-1.080). Confounding factors (ovum donation or autologous cycles; day-3 or blastocyst embryo transfer [ET]; natural or hormonal replacement therapy for ET; single or double ET; previous cycles, number of oocytes, doses of gonadotropins and E2 levels on the day of hCG) did not modify the effect of double vitrification on DR (OR 0.872, 95% CI 0.702-1.084).

Conclusion(s): Vitrification at early cleavage or blastocyst stage of embryos obtained from previously vitrified oocytes has no effect on DR/warming cycle.