ASSESSMENT OF POLYPLOIDY IN HUMAN MORULAE AND BLASTOCYSTS USING COCULTURE AND FLUORESCENT INSITU HYBRIDIZATION

Fluorescence in-situ hybridization with DNA probes for X, Y and no. 18 chromosomes was used to analyse human morulae (n = 13) and blastocyst s (n = 41), obtained after co-culture on Vero cells. On the basis of t he number of hybridization signals, the proportion of embryos with mor e than five polyploid cells was 30.8% for morulae and 29.3% for blasto cysts. These values are similar to those for mixoploidy (mosaicism of diploid and polyploid cells) observed in blastocysts of animal species . The results were confirmed by scanning electron microscopy, which sh owed a wide variation in the size of blastocyst nuclei, and by classic al cytogenetic analysis. Mixoploidy seems to be a normal feature in pr eimplantation embryos and to occur very early in human embryo developm ent. This lays open to doubt the preimplantation diagnosis of genetic errors at these stages, since results obtained from single cell analys is may not be representative of the whole embryo.