Journal Article

The development of cytogenetically normal, abnormal and mosaic embryos: a theoretical model

Frans J. Los, Diane Van Opstal and Cardi van den Berg

in Human Reproduction Update

Published on behalf of European Society of Human Reproduction and Embryology

Volume 10, issue 1, pages 79-94
Published in print January 2004 | ISSN: 1355-4786
Published online January 2004 | e-ISSN: 1460-2369 | DOI:
The development of cytogenetically normal, abnormal and mosaic embryos: a theoretical model

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  • Critical Care
  • Reproductive Medicine


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Assisted reproduction and preimplantation genetic diagnosis (PGD) involve various complicated techniques, each of them with its own problems. However, the greatest problem with PGD for chromosome abnormalities is not of a technical nature but is a biological phenomenon: chromosomal mosaicism in the cleavage stage embryo. Here, we present a hypothetical, quantitative model for the development of chromosomally normal, abnormal and mosaic embryos. The arising of mosaicism in 2–8‐cell embryos was described by a binomial probability model on the occurrence of mitotic events inducing chromosomal changes in the blastomeres. This model converted the ‘mean’ rate of mosaicism found in cross‐sectional studies (60%) into an equal rate of mosaic embryos at arrival at the 8‐cell stage (59.8%). The disappearance of >90% of the mosaic embryos or the mosaicism itself from surviving embryos during the morula stage was explained by mitotic arrest of most of the mitotically changed cells under increasing cell cycle control. In our model, 25.9 and 14.3% of the embryos at the 8‐cell stage are normal and abnormal respectively. The remaining 59.8% of the embryo shows mosaicism: 34.6% of abnormal/normal cells and 25.2% of abnormal/abnormal cells. The high proportion of abnormal and mosaic embryos together explains the high rate of abnormal laboratory findings in PGD for chromosomal abnormalities and aneuploidy screening. The poor representation of a 1‐ or 2‐cell biopsy for the 7‐ or 6‐cell post‐biopsy embryo in the case of mosaicism explains the high rate of false‐negative and false‐positive results.

Keywords: chromosomal mosaicism/embryo/model/preimplantation genetic diagnosis/uniparental disomy

Journal Article.  15301 words.  Illustrated.

Subjects: Critical Care ; Reproductive Medicine

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