The developmental potential of cryopreserved human embryos

Using rigorously matched non-frozen controls we have shown that cryopreserv ation does not alter the implantation potential of early cleavage stage (da y 2) human embryos if no blastomere loss occurs. Thawed intact 4-cell embry os have a significantly higher implantation (fetal heart) rate (16.9%) than similar 2-cell embryos (7.2%). This difference is not due to blastomere nu mber per se since increasing the cell number in frozen embryos by allowing an extended period in culture prior to freezing does not alter their intrin sic developmental potential. Blastomere loss, which occurred in almost half of all thawed embryos, is directly related to a reduction in developmental potential. We estimate that approximately 30% of the expected fresh embryo implantations are lost as a consequence-of cryopreservation. Both preimpla ntation and peri-implantation losses may contribute to this outcome. (C) 20 00 Elsevier Science Ireland Ltd. All rights reserved.