The recent development of co-culture technique has permitted to cryopreserve human embryos at the blastocyst stage. The aim of the present study was to compare pregnancy rates after transfers of embryos frozen at an early embryo stage (2-8 cell stage, group A; n = 175) with others frozen at blastocyst stage (group B; n = 98). Our results demonstrated that the frozen/thawed blastocyst survival is approximately 100%. In comparison the early embryos survival rate was 59% (P < 0.05). Moreover, pregnancy rates/embryo transfer in group A (16.4%) were significantly improved by comparison to those observed with early embryos (6.2%) (P < 0.05). In conclusion, our results demonstrate that embryo frozen/thawed at the blastocyst stage can be useful for improving pregnancy rates after cryopreservation.