Fertilization and early embryolgoy: A comparison of the effects of different biopsy strategies on the post-thaw survival of 8-cell-stage mouse embryos: implications for preimplantation diagnosis

The aim of this study was to investigate the effects of twodifferent biopsy strategies, zona slitting and zona piercing,on the post-thaw survival and subsequent in-vitro developmentof 8-cell mouse embryos. From control experiments it was determinedthat neither biopsy by zona slitting nor zona piercing adverselyaffected embryo development in vitro, as similar rates of blastocystformation and hatching were found between biopsied and zona-intactembryos; there was, however, a trend towards a lower rate ofblastocyst hatching in embryos biopsied by zona piercing (78.3%compared with 91.9% of zona-intact embryos). When biopsy wasfollowed by cryopreservation a different picture was seen: similarrates of freeze—thaw survival were found for zona-slit,zona-pierced and zona-intact embryos (84.2, 88.5 and 87.2% respectively),but this was superseded by a significant (P < 0.05) reductionin the blastocyst formation rates (61.4% zona-slit and 63.9%zona-pierced versus 78.7% zona-intact) and hatching rates (51%zona-slit and 52.5% zona-pierced versus 72.3% zona-intact) ofthe biopsied embryos. When the effects of zona slitting andpiercing were considered in isolation, i.e. without performingbiopsy, it was found that the larger holes produced by zonaslitting rendered embryos more susceptible to freeze-thaw damage.Significant (P < 0.05) reductions occurred in the blastocystformation rates (63.7% zona-slit versus 78.7% zona-intact embryos)and hatching rates (52.3% zona-slit versus 72.3% zona-intactembryos) of the zona-slit embryos.