Cryoloop vitrification of human day 3 cleavage-stage embryos: post-vitrification development, pregnancy outcomes and live births

Vitrification technology has shown great promise for cryopreservation of human embryos. The majority of this work has been with blastocyst-stage embryos. This report describes initial clinical results following vitrification of human embryos on day 3 of culture at the 6- to 8-cell stage. A total of 236 embryos were cryopreserved on cryoloops using a vitrification protocol. Warmed embryos were cultured until day 5 before transfer to the patient. The post-warming survival rate was 85%. The clinical pregnancy rate was 44% (34/77), and the implantation rate was 20% (40/201). In transfers where at least one warmed embryo reached the blastocyst stage by the day of transfer, the clinical pregnancy rate was 58% (28/48). The cryoloop was an excellent vessel for ultra-rapid cryopreservation of embryos. This study supports the effectiveness of a dimethylsulphoxide/ethylene glycol cryoprotectant combination for vitrification of human embryos at the 6- to 8-cell stage.