FISH reanalysis on day 6 blastocysts diagnosed as aneuploidy on day 3: does day 3 single cell analysis accurately represent the numerical chromosomal status of the embryo?

Abstract

Six hundred sixty human embryos from 94 IVF/ICSI cycles were biopsied on Day 3 and a single blastomere removed for identification of the five chromosomes 13, 18, 21, X and Y (those most involved in human aneuploidy) by Fluorescent in Situ Hybridization (FISH). 367(55.6%) of the embryos were euploid and 213 embryos were transferred in 85 patients. The average number of embryos transferred was 2.5 per patient. 44 patients were pregnant (51.8%/ET). 281 (42.6%) embryos were diagnosed as aneuploid. 86 normal embryos left over from transfer and all 281 aneuploid embryos were further cultured to Day 6. Aneuploid embryos are more likely to arrest (73.7%) before day 6 than normal embryos (37.2%) at extended culture (p<0.01). In the normal group, 54(62.8%) went to blastocyst/morula, whereas 74(26.3%) in the aneuploid group developed to blastocyst (56, 19.9%)/morula. Chromosomal reanalysis for the same probes of the Inner Cell Mass of the aneuploid group blastocysts confirmed that 34(60.7%) were aneuploid (trisomy, polyploidy or monosomy) that were concordant from D3 single cell diagnosis, 22(39.3%) of the blastocysts were diploid. The reason for this non-predictable outcome is due not only to FISH errors such as overlapped signals, hybridization failure, or nuclear material lost during either slide fixation or FISH. We believe mosaicism of the D3 embryo is a significant cause of this non-concordance and that the embryo has limited self-correction abilities in its development.