Viability of partially damaged human embryos after cryopreservation

In our centre, embryos are judged to have survived cryopreservation if atleast half of the initial number of blastomeres remain intact. Thereforeboth fully intact and partially damaged embryos are transferred. The aim ofthis study was to investigate the viability of partially damaged humanembryos after cryopreservation. We retrospectively analysed theimplantation and in-vivo development of embryos which were either fullyintact or had lost some blastomeres after cryopreservation. Oocytes werecollected following stimulation with the gonadotrophin-releasing hormone(GnRH)-agonist Buserelin and human menopausal gonadotrophin. Supernumerarymulticellular embryos with not more than 20% of their volume filled withanucleate fragments were frozen on day 2 or day 3 of the cycle using a slowcooling procedure with dimethylsulphoxide as the cryoprotectant. Followingslow thawing, 431 fully intact embryos were transferred in 314 embryotransfer procedures and 488 partially damaged embryos were transferred in327 such procedures. The percentage of gestational sacs with fetalheartbeat obtained after transfer of fully intact embryos was almost threetimes higher than that after transfer of partially damaged embryos (11.4versus 3.5%). Forty-five children (birth rate 10% per embryo transfer) wereborn after transfer of fully intact embryos and 14 after transfer ofembryos from which some blastomeres had been lost followingcryopreservation. In conclusion, although children have been deliveredafter transfer of partially damaged embryos, the aim of a cryopreservationprogramme must be to obtain fully intact embryos after thawing.