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.