Chromosomal constitution of embryos derived from tripronuclear zygotes studied by fluorescence in situ hybridization using probes for chromosomes 4, 13, 18, 21, X, and Y.

This study was designed to assess the chromosomal constitution and segregation patterns of cleaving embryos derived from tripronuclear zygotes. Thirty-two embryos obtained from 19 conventional IVF patients were analyzed by fluorescence in situ hybridization (FISH) using probes for chromosomes 4, 13, 18, 21, X, and Y. Sixteen embryos (50.0%) exhibited uniform, non-mosaic patterns. These embryos showed pure triploid (n = 7), pure diploid (n = 7), or pure haploid (n = 2). The remaining 16 embryos showed mosaic patterns; 1 was triploid-diploid mosaics, 9 were diploid-haploid, and 4 were haploid only. Autosomal aneuploidy occurred in 2 embryos showing a triploid complement. The sex chromosomal constituent XXX:XXY:XYY was 3:4:2 in embryos showing a pure triploid complement (including 2 embryos with aneuploidy). This ratio was not significantly different from the expected 1:2:1 (p = 0.96). Pure triploid was found in 41.7% of 2-cell embryos, but no triploid complement was found in 3-cell embryos. The present study also supports the diandric origin of tripronuclear zygotes in the conventional IVF, and, to our knowledge, is the first study to use simultaneous six-color FISH for chromosomes 4, 13, 18, 21, X, and Y in human embryos. However, no additive information was obtained about chromosome 4. Copyright 2005 S. Karger AG, Basel.