Undocumented embryos: do not trash them, FISH them.

Pronuclei formation is routinely assessed 16-20 h after oocyte insemination in in-vitro fertilization (IVF). Occasionally, the pronuclei disappear before this time, rendering them as 'undocumented'. Since the number of pronuclei detected is used to distinguish normal from abnormal embryos in the context of ploidy, the diploidy of undocumented embryos is questionable, and therefore they are routinely discarded. The introduction of fluorescent in-situ hybridization (FISH) technology allows the assessment of ploidy status in undocumented embryos that continue to cleave to form blostomeres. In this study, we used FISH to analyse the chromosomal status of 23 undocumented embryos obtained from 10 patients. Biopsied blastomeres were fixed and probed for five chromosomes (X, Y, 13, 18, 21). Diploidy was confirmed in 13 (57%) embryos while the remaining 10 embryos displayed various chromosomal anomalies. Six of the diploid embryos were transferred subsequently to the patients. One ongoing pregnancy was achieved following transfer of an undocumented, analysed embryo, which was already cleaved when assessed 20 h after insemination. We suggest that accelerated dismantling of the pronuclear membrane and subsequent cleavage do not necessarily indicate abnormal chromosomal content and may result in normal pregnancy. In a patient with a small number of embryos, FISH may be used to ascertain diploidy of undocumented embryos, thereby increasing the number of available embryos for transfer.