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The relationship between chromosomal abnormality in the human preimplantation embryo and development in vitro.

The relationship between the survival of the human preimplantation embryo in vitro and chromosomal abnormality was investigated by cytogenetic analysis of a total of 250 embryos of varying morphology between the pronucleate stage and the 8-cell stage. The overall incidence of chromosomal abnormality among these embryos was 49%. At the pronucleate stage (n = 46) the incidence was 65.2%, at the 2-4-cell stage (n = 126) it was 54.6%, and at the 5-8-cell stage (n = 78) it was 27.4%. Cleavage-stage embryos with poor morphology (irregular shaped blastomeres with severe extracellular fragmentation) showed a higher incidence of chromosomal abnormality (62%; 54 of 87 analysed) than those with good morphology (22.2%; 26 of 117 analysed). This study demonstrates: (i) that there is progressive loss of chromosomally-abnormal embryos during preimplantation development; and (ii) that there is an association between chromosomal abnormality and embryo morphology.