The incidence of mitotic abnormalities in cryopreserved eight-cell early and compacted mouse embryos

The effects of slow freezing-rapid thawing on viability and chromosomal complement of eight-cell early and eight-cell compacted mouse embryos were investigated. The abnormalities connected with damage to the mitotic apparatus, and with chromosome damage were investigated in cryopreserved embryos by cytological analysis. The embryos were preserved using 1M glycerol as cryoprotectant and a slow cooling regime to -30ºC before transfer to liquid nitrogen. The proportion of mitotic abnormalities in compacted embryos was significantly higher (13.1%) than in early embryos (5.9%) and unfrozen control embryos (3.9%) in these studies performed after thawing. This was reflected after cryopreservation by a reduced viability of the embryos as judged by culture to the hatching blastocyst stage – compacted 8-cell embryos (71.8±4.7%) versus controls (78.4±5.9%) and cryopreserved early-stage 8-cell embryos (86.1±4.0%) – P<0.05 in each case. However, aneuploidy rates were low in all groups in both fresh and cryopreserved embryos (around 3%).