Fertilization and early embryology: Undocumented embryos: do not trash them, FISH them

Abstract

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.

Live births resulting from 0PN-derived embryos in conventional IVF cycles

“…In this study, 11.3 % 0PN-derived embryos were observed with an average age of 32.8 comparable with our general patient population, suggesting that aging is not a significant contributory factor to the occurrence of 0PN-derived embryos. This finding is consistent with previous reports [6].…”

“…It has been reported that the percentage of embryos from 0PN oocytes may vary from 12.7 to 20 % of day 3 embryos [6]. In this study, 11.3 % 0PN-derived embryos were observed with an average age of 32.8 comparable with our general patient population, suggesting that aging is not a significant contributory factor to the occurrence of 0PN-derived embryos.…”

“…The rationale in allowing the transfer of 0PN-derived embryos is that 0PN oocytes might be bipronucleated and develop into euploid embryos, but due to differences in cell cycle timing, pronuclei were not visible at the time of the fertilization check [6]. In this study, 0PN-derived embryos were more likely to be observed in good prognosis patients, i.e., younger patients with a good ovarian stimulation response.…”

“…There are a number of studies regarding chromosome abnormalities of 0PN-derived embryos versus 2PN embryos. A fluorescent in situ hybridization (FISH) study found that 57 % (13/23) of embryos defined as 0PN at the fertilization check formed diploid embryos, six of which displayed a Y chromosome signal [6]. In contrast, Nicole Noyes et al reported a FISH analysis for a number of chromosomes.…”

“…On the other hand, 2PN zygotes are not necessarily euploid. Furthermore, there are reports of 0PN-derived embryos present in 12 to 20 % of day 3 embryos [3][4][5] which result in healthy babies [4,6,7]. Although to transfer such embryos in the absence of the signs of normal fertilization may have become an option in clinical policy, it is still a dilemma for the clinical team when it comes to carrying this out in practice.…”