Background: FISH (Fluorescent In Situ Hybridization) analysis is often used to determine the chromosomal status of the embryo in patients undergoing PGD (Preimplantation Genetic Diagnosis).

Objective: The purpose of this study was to determine the accuracy of FISH as well as to determine which abnormalities are most frequently confirmed.

Materials and Methods: All embryos determined to be abnormal by PGD, or normal but unsuitable for cryopresevation, which would have otherwise been discarded, were included. These embryos were fixed one to three days after PGD and FISH analysis was performed on all nuclei that were fixed. 178 embryos were included in the study from 70 IVF patients that had PGD. Single blastomeres were biopsied on day 3 and chromosomes 13, 18, 21, X and Y were analyzed by FISH. Euploid embryos were transferred back on day 4-6 post-retrieval or cryopreserved. The abnormal embryos or normal embryos that were not suitable for cryopreservation, that would have otherwise been discarded, were used for this study after patient consent was obtained.

Results: Out of the 146 embryos diagnosed as abnormal on day 3, 122/146 (84%) of them were confirmed abnormal on confirmation FISH. The exact day 3 diagnosis was confirmed in 70/146 embryos (48%) while 24/146 embryos (16%) were deemed as normal on reconfirmation (the criteria of normal: if the embryo has more than 50% normal cells). Thirty-two embryos were determined to be chromosomally normal by single cell and day 3 FISH analysis was performed. These embryos would have otherwise been discarded due to poor morphology or arrested growth between day 3-6 culture, and 27/32 of them (84%) were confirmed as normal when FISH reconfirmation was done. Therefore the positive and negative predictive values were both 84%. Monosomies and trisomies were the most common abnormalities on day 3 that were also confirmed on repeat FISH. (see table 1)

Table 1.

Day 3 diagnosis	# of embryos normal on confirmation FISH	# of embryos abnormal and diagnosis confirmed on confirmation FISH	# of embryos Abnormal but diagnosis not confirmed
Monosomy (N=28)	2 (7%)	23 (82%)	3 (11%)
Trisomy (N=28)	2 (7%)	20 (72%)	6 (21%)
Tetrasomy (N=4)	0	2 (50%)	2 (50%)
Polyploidy (N=13) (includes triploid, polyploidy)	3 (23%)	5 (38.5%)	5 (38.5%)
Turner (N=7)	5 (72%)	1 (14%)	1 (14%)
2 abnormalities (N=23)	4 (17%)	9 (39%)	10 (44%)
More than 2 abnormalities (N=15) (includes haploid)	3 (20%)	3 (20%)	9 (60%)
Nuclear fragments-abnormal (n=20)	1 (5%)	5 (25%)	14 (70%)
Other mixed abnormalities (N=8) (includes split, overlap, unclear signals, Nuclear fragments normal, Nuclear fragments-normal and abnormal)	4 (50%)	2 (25%)	2 (25%)

Conclusion: FISH analysis of day 3 blastomeres has a positive and negative predictive value of 84% in patients that undergo PGD. Certain abnormalities such as monosomies and trisomies are less likely to be falsely diagnosed as abnormal compared to other abnormalities such as Turner syndrome.

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