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OBJECTIVE: To determine the effects of zona slitting and subsequent embryo transfer performed on different days of in vitro human embryonic development to allow appropriate application of assisted hatching techniques to clinical IVF-ET. DESIGN: A microsurgical technique was used to make a standardized slit in the zona pellucida of bipronucleate human embryos on day 2, 3, or 5 after oocyte retrieval. A mock ET was performed after the procedure and the rate of blastocyst formation and the process of hatching in each embryo was monitored. SETTING: All embryos used were donated for research by patients attending the IVF Unit at the John Radcliffe Hospital, Oxford, United Kingdom. MAIN OUTCOME MEASURES: The effects of the mock ET on the integrity of zona-slit embryos was documented. The embryos were cultured further and parameters such as blastocyst formation, initiation, and completion of hatching were monitored in all three groups of embryos. RESULTS: The mock ET did not have a detrimental effect on embryos as assessed by their morphology and subsequent blastocyst formation rate. The technique used in this study to make an opening in the zona increased the rate and number of blastocysts hatching in all three groups compared with nonmanipulated controls. However, the day on which the slit was made did not significantly alter the outcome. CONCLUSION: A gap in the zona pellucida of human embryos significantly increases the rate of hatching. Micromanipulative techniques such as zona slitting can be suitably used for this purpose without loss of blastomeres through the gap in the zona or trapping of the embryo during the process of hatching.


Journal article


Fertil Steril

Publication Date





514 - 520


Blastocyst, Embryo Transfer, Embryo, Mammalian, Embryonic and Fetal Development, Female, Fertilization in Vitro, Humans, Micromanipulation, Zona Pellucida