Preimplantation genetic testing for aneuploidy (PGT-A): The biology, the technology and the clinical outcomes.

Preimplantation genetic testing for aneuploidy (PGT-A) seeks to identify preimplantation embryos with a normal chromosome complement (euploid) during in vitro fertilisation (IVF). By sifting out embryos with abnormal chromosome numbers (aneuploid), PGT-A should theoretically improve pregnancy success. However, earlier versions of PGT-A were ineffective, and in some cases, detrimental, due to biopsy-induced trauma and because the technology at the time could analyse only a fraction of all chromosomes. More recently, the emergence of technologies enabling all chromosomes to be analysed and a switch to less traumatic blastocyst-stage biopsy have seen widespread uptake of PGT-A. Assessing the full impact of blastocyst biopsy PGT-A requires consideration of multiple factors, including embryonic mosaicism, sensitivity of the technological platform used, embryo loss during long-term in vitro culture, embryo cryopreservation and inter-clinic variability in expertise. Significantly, there hasnt yet been an appropriately designed randomised controlled trial (RCT) of blastocyst biopsy PGT-A analysed by intention-to-treat that accounts for all these parameters on a per-cycle basis. The three RCTs reporting benefits studied outcomes on a per-embryo transfer basis were small and underpowered and demonstrated benefits for a very select sub-group of good prognosis patients. The liberal use of this very expensive IVF add-on for other patient populations has not yet been shown to be effective, or indeed, without harm.