Vitrification of human blastocysts previously cryopreserved by slow controlled-rate freezing at the cleavage stage

The objective of this study was to evaluate the efficiency of vitrified blastocysts derived from frozen-thawed cleavage stage embryos in terms of morphological survival and re-expansion status of the blastocoelic cavity.

After warming 162 blastocysts derived from fresh embryos (= control group) and 90 blastocysts from frozen-thawed cleavage stage embryos (= study group) and after 2-3 h of in vitro culture the percentage of blastocysts with morphological survival was not different between the two groups. After 24 h of in vitro culture, the percentage of fully expanded, hatching or hatched blastocysts was not different between both groups.

The results show that blastocysts derived from frozen-thawed cleavage stage embryos can be cryopreserved successfully a second time by vitrification method. Re-cryopreservation by vitrification still needs to be approached with some caution because little data on long term safety of multiple freezing is available.