Accuracy of preimplantation genetic screening (PGS) is compromised by degree of mosaicism of human embryos

Abstract

BackgroundTo preclude transfer of aneuploid embryos, current preimplantation genetic screening (PGS) usually involves one trophectoderm biopsy at blastocyst stage, assumed to represent embryo ploidy. Whether one such biopsy can correctly assess embryo ploidy has recently, however, been questioned.MethodsThis descriptive study investigated accuracy of PGS in two ways. Part I: Two infertile couples donated 11 embryos, previously diagnosed as aneuploid and, therefore, destined to be discarded. They were dissected into 37 anonymized specimens, and sent to another national laboratory for repeat analyses to assess (i) inter-laboratory congruity and (ii) intra-embryo congruity of multiple embryo biopsies in a single laboratory. Part II: Reports on human IVF cycle outcomes after transfer of allegedly aneuploid embryos into 8 infertile patients.ResultsOnly 2/11 (18.2 %) embryos were identically assessed at two PGS laboratories; 4/11 (36.4 %), on repeat analysis were chromosomally normal, 2 mosaic normal/abnormal, and 5/11 (45.5 %) completely differed in reported aneuploidies. In intra-embryo analyses, 5/10 (50 %) differed between biopsy sites. Eight transfers of previously reported aneuploid embryos resulted in 5 chromosomally normal pregnancies, 4 delivered and 1 ongoing. Three patients did not conceive, though 1 among them experienced a chemical pregnancy.ConclusionsThough populations of both study parts are too small to draw statistically adequately powered conclusions on specific degrees of inaccuracy of PGS, here presented results do raise concerns especially about false-positive diagnoses. While inter-laboratory variations may at least partially be explained by different diagnostic platforms utilized, they cannot explain observed intra-embryo variations, suggesting more frequent trophectoderm mosiaicsm than previously reported. Together with recentl published mouse studies of lineages-specific degrees of survival of aneuploid cells in early stage embryos, these results call into question the biological basis of PGS, based on the assumption that a single trophectoderm biopsy can reliably determine embryo ploidy.

Should preimplantation genetic screening (PGS) be implemented to routine IVF practice?

“…Overall, 8/22 biopsies (36.6 %) revealed either mosaicism or inconclusive results. Also supporting above described mouse study, two independent groups reported surprisingly high live birth rates of healthy, genetically normal infants after transfer of embryos after PGS 2.0 reported to be aneuploid (mosaic) [15,16]. These results are indicative of significant false-positive rates following PGS 2.0 and raise serious concerns about the potential discarding of perfectly normal embryos in large quantities in current PGS 2.0 utilization.…”

Embryo wastage rates remain high in assisted reproductive technology (ART): a look at the trends from 2004–2013 in the USA

“…In the group of women older than 40 years studies with PGS on trophoblast cells have shown that a large number of embryos produced are chromosomally abnormal, thus explaining at least in part why there is such high BEmbryo Wastage^in this age group [16,34]. However, it remains to be seen whether this technique will ultimately lead to a significant improvement in live birth rate since it is still error-prone with the risk of discarding embryos wrongly diagnosed as aneuploidy because of mosaicism [21][22][23]. Other barriers such as the cost, including the possible need to cryopreserve embryos and defer transfer, and invasiveness of the biopsy and any potential long term effects also need to be addressed.…”

“…Recent improvements in pre-implantation genetic screening (PGS) techniques for identifying normal euploid embryos have been associated with higher pregnancy and delivery rates when analyzed per transfer [15][16][17]; however, several barriers to its widespread use still exist, including cost and particularly the lack of unequivocal evidence that its use improves pregnancy and live birth rates, particularly for patients with few embryos available for testing, due to the presence of high rates of mosaicism in the trophoblast cells [18][19][20][21][22][23]. Other studies have reported on the use of proteomics and metabolomics to identify factors in embryo culture media that may be predictive of embryo competence or assessing gene expression in cumulus cells; however, even these methods are still inefficient and not ready yet for clinical application [24][25][26][27].…”

Mosaicism: throwing the baby out with the bath water?

“…More recently, Tortoriello et al performed a second trophectoderm biopsy in embryos initially deemed by cytogenetics to be aneuploid and found that 9/27 (33 %) were euploid when using a different technology and a different genetic laboratory [18]. Gleicher et al found a similar false positive rate (36.4 %) when re-testing dissected embryos initially reported as aneuploid [19]. To date, studies have reported similar miscarriage rates in patients undergoing in vitro fertilization when compared to a sub-fertile population; thus, even if some laboratory conditions are correlated with increases in postfertilization mosaicism, that does not automatically correlate to an increase in miscarriages [20].…”