[Comparison of vitrification and slow-freezing of human day 3 cleavage stage embryos: post-vitrification development and pregnancy outcomes].

Objective: To compare the effects of vitrification with slow-freezing on the developmental ability of day 3 cleavage stage embryos.
Methods: Patients who had no less than 4 high quality embryos were included in this study. These embryos were cryopreserved using the methods of vitrification or slow-freezing. In the cryopreserved embryo transfer cycles, the embryos which were cryopreserved using one of the methods were chosen randomly. The developmental ability of embryos was compared between these two groups.
Results: A total of 80 patients were included in this study with 160 embryos. In the group of slow-freezing, 73 (91%) embryos were survived and achieved 15 (38%) clinical pregnancies. Among these, 3 were twins and the implantation rate was 25% (18/73). In the group of vitrification, 71 (89%) embryos were survived and achieved 19 (48%) clinical pregnancies. Among these, 9 were twins and the implantation rate was 39% (28/71), which was significantly higher than the slow-freezing group (P < 0.05). Otherwise, the clinical pregnant rate and multiple pregnant rate was higher in the group of vitrification than the slow-freezing group, but had no significance.
Conclusion: Vitrification is more benefit for the developmental ability of the thawed embryos and more suitable for the cryopreservation of day 3 cleavage stage embryos.