The clinicians' dilemma with mosaicism-an insight from inner cell mass biopsies

STUDY QUESTION: How reliable are cleavage stage and trophectoderm (TE) biopsies compared to inner cell mass (ICM) biopsies? SUMMARY ANSWER: The reliability of TE biopsy compared to ICM biopsy is almost perfect, but only substantial between cleavage stage biopsy and ICM biopsy. WHAT IS KNOWN ALREADY: One of the prevailing reasons for implantation failure is presumed to be chromosomal aneuploidy in human preimplantation embryos. Preimplantation genetic testing for aneuploidies (PGT-A) has been introduced into assisted reproduction in an effort to increase pregnancy rates. Increasing evidence indicates that genetic results obtained following blastomere or TEbiopsy may not accurately reflect the true genetic status of the embryo due to the presence of embryonic mosaicism, and therefore the reliability of PGT is highly controversial. STUDY DESIGN, SIZE, DURATION: This was an observational descriptive study, performed in a private infertility centre from August 2016 to January 2017. PARTICIPANTS/MATERIALS, SETTING, METHODS: The mean female age was 33.9 years, ranging from 24 to 46 years, and the mean number of biopsied embryos per couple was 2.2 (range 1-7 embryos). Blastomere biopsies had been performed at cleavage stage on Day 3 (D3) due to the turnover time of genetic testing and the inability to cryopreserve embryos in accordance with the local law governing ART. To confirm the genetic results in embryos not chosen for transfer, additional biopsies of the TE at blastocyst stage (BLASTO-TE) as well as of the ICM (BLASTO-ICM) were performed on D5. Only surplus blastocysts, which had not been selected for transfer and were not cryopreserved in accordance with the law governing ART, had been included. MAIN RESULTS AND THE ROLE OF CHANCE: Comparison of all biopsies (D3/BLASTO-ICM/BLASTO-TE) per embryo demonstrated that 50 (59.5%) out of 84 embryos showed concordance in all three results (= full concordance). Thirty-four (40.4%) embryos had at least two discordant results between the three biopsies, regardless of whether the embryo diagnosis (aneuploid/euploid) was discordant or not, or in aneuploid embryos, whether the chromosomal patterns were inconsistent. Nine (= 10.7%) embryos had complete discordance between all three biopsies. False positive results between D3/BLASTO-TE, D3/BLASTO-ICM and BLASTO-TE/BLASTO-ICM were 26.4%/30.2% and 7.5%, respectively, while the Kappa agreement between the different approaches was 0.647, 0.553 and 0.857, respectively. Therefore the reliability of D3/BLASTO-TE, D3/BLASTO-ICM and BLASTO-TE/BLASTO-ICM can be interpreted as substantial, as moderate and as almost perfect. LIMITATIONS, REASONS FOR CAUTION: The limitation of this study is the possible bias in the concordance/discordance rate because embryos that had been selected for transfer did not undergo biopsy on D5. WIDER IMPLICATIONS OF THE FINDINGS: The obvious discordance between the three different approaches for PGT-A underlines the limitations of genetic testing and highlights the importance of ongoing research in order to improve the accuracy of PGT-A results. Until then reproductive specialists will continue to make challenging decisions on whether to transfer or discard an embryo in light of current evidence questioning the reliability of genetic results.