The influence of in-vitro development upon post-thaw survival and implantation of cryopreserved human blastocysts

Blastocysts from 198 patients were frozen using glycerol ascryoprotectant. No difference in the post-thaw survival of blastocystsor implantation rates was found between 177 patients (122 transfers)with all surplus embryos cultured to blastocysts before freezingand 20 patients (12 transfers) whose embryos were consideredunsuitable for freezing during cleavage and were then frozenas blastocysts. Nineteen pregnancies were achieved, of whichsix aborted. Pre-freezing morphology was similar in blastocystsof patients in groups 1 and 2 and did not relate to their survivalafter cryopreservation. A significantly lower proportion withsuspected damage after thawing was present among patients becomingpregnant after transfers of single blastocysts (P < 0.01)and implanting embryos were in general more expanded at thetime of transfer. No differences were detected between blastocystsresulting in normal development and those leading to abortion.The developmental consequences of damage to human blastocystsare discussed.