Microscopic assessment of pronuclear embryos is not definitive

The microscopic classification of embryos, especially unipronuclear embryos , is not very precise. A number of undocumented and unipronuclear embryos w ere determined to be diploid following karyotyping and fluorescence in situ hybridization (FISH). accelerated and asynchronous pronuclear dismantling at the time of checking for embryo fertilization accounts for this disparit y. Diploid embryos were also observed among tripronuclear embryos. However, not all embryos ascertained as diploid by FISH were karyotypically normal following full karyotype analysis. By taking into account the "background" abnormality rate, the rate of diploid embryo wastage was estimated to be ab out 40% among undocumented embryos and about 58% in total. A high percentag e of misclassification infers an unintended loss of otherwise transferable embryos. Such a discrepancy is particularly important to older women who ha ve fewer embryos. If these ale a woman's only embryos, preimplantation gene tic diagnosis might be applicable in determining those that are diploid and suitable for transfer. This could potentially reduce the number of wasted embryos and cycles. The pre sent study has also shown that mosaicism is com mon but it is still unclear whether mosaicism is indicative of embryonic ab normality or is a fairly common phenomenon among healthy embryos. Bipronucl ear embryos that pre sent with abnormal or delayed cleavage are often chaot ic in their chromosomal constitution. Such embryos should not be transferre d.