A randomized controlled trial comparing two vitrification methods versus slow-freezing for cryopreservation of human...

To compare two different vitrification methods to slow freezing method for cryopreservation of human cleavage stage embryos.

Prospective randomised trial.

University assisted reproduction centre.

568 patients (mean age 33.4 ± 5.2) from April 2009 to April 2011.

1798 supernumerary good-quality cleavage stage embryos in 645 IVF cycles intended to be cryopreserved were randomly allocated to three groups: slow freezing, vitrification with the Irvine® method, vitrification with the Vitrolife® method.

Embryo survival and cleavage rates, implantation rate.

A total of 1055 embryos were warmed, 836 (79.2%) survived and 676 were finally transferred (64.1%). Post-warming embryos survival rate was significantly higher after vitrification (Irvine: 89.4%; Vitrolife: 87.6%) than after slow freezing (63.8%) (p < 0.001). No differences in survival rates were observed between the two vitrification methods, but a significant higher cleavage rate was observed using Irvine compared to Vitrolife method (p < 0.05). Implantation rate (IR) per embryo replaced and per embryo warmed were respectively 15.8% (41/259) and 12.4% (41/330) for Irvine, 17.0% (40/235) and 12.1% (40/330) for Vitrolife, 21.4% (39/182) and 9.9% (39/395) for slow-freezing (NS).

Both vitrification methods (Irvine and Vitrolife) are more efficient than slow freezing for cryopreservation of human cleavage stage embryos in terms of post-warming survival rate. No significant difference in the implantation rate was observed between the three cryopreservation methods.