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 two different biopsy strategies, zona slitting and zona piercing, on the post-thaw survival and subsequent in-vitro development of 8-cell mouse embryos. From control experiments it was determined that neither biopsy by zona slitting nor zona piercing adversely affected embryo development in vitro, as similar rates of blastocyst formation and hatching were found between biopsied and zona-intact embryos; there was, however, a trend towards a lower rate of blastocyst hatching in embryos biopsied by zona piercing (78.3% compared with 91.9% of zona-intact embryos). When biopsy was followed by cryopreservation a different picture was seen: similar rates 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were found for zona-slit, zona-pierced and zona-intact embryos (84.2, 88.5 and 87.2% respectively), but this was superseded by a significant (P 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) reduction in 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) of the biopsied embryos. When the effects of zona slitting and piercing were considered in isolation, i.e. without performing biopsy, it was found that the larger holes produced by zona slitting rendered embryos more susceptible to freeze-thaw damage.(ABSTRACT TRUNCATED AT 250 WORDS)