Response: how PGS/PGT-a laboratories succeeded in losing all credibility.

Abstract

We commend the passion with which Dr Gleicher et al, 2018Gleicher N. Kushnir A. Barad D.H. How PGS/PGT-A laboratories succeeded in losing all credibility.Reprod. Biomed. Online. 2018; 37: 242-245Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar defend their business model, denouncing preimplantation genetic screening (PGS) as their marketing differentiator from other centres. It would be idealistic if this was a purely academic discussion, however there are commercial interests on both sides and whilst the authors discuss theories and opinions, this reply reports facts and data supporting PGS. The scientific evidence that euploid embryos have higher ongoing pregnancy rates per transfer than embryos replaced at random in patients 35 and older is overwhelming (Forman et al, 2013Forman E.J. Hong K.H. Ferry K.M. Tao X. Taylor D. Levy B. Treff N.R. Scott R.T. In vitro fertilization with single euploid blastocyst transfer: a randomized controlled trial.Fertil. Steril. 2013; 100: 100-107Abstract Full Text Full Text PDF PubMed Scopus (382) Google Scholar, Munné et al, 2017aMunné S. Kaplan B. Frattarelli J. Gysler M. Child T. Nakhuda G. Shamma F.N. Silverberg K. Kalista T. Oliver K. Katz-Jaffe M. Wells D. Gordon T. Willman S. Global multicenter randomized controlled trial comparing single embryo transfer with embryo selection by preimplantation genetic screening using next-generation sequencing versus morphologic assessment.Fertil. Steril. 2017; 108 (O-43): e19Abstract Full Text Full Text PDF PubMed Google Scholar, Rubio et al, 2017Rubio C. Bellver J. Rodrigoa L. Castillon G. Guillen A. Vidal C. Giles J. Ferrando M. Cabanillas S. Remohí J. Pellicer A. Simón C. In vitro fertilization with preimplantation genetic diagnosis for aneuploidies in advanced maternal age: a randomized controlled study.Fertil. Steril. 2017; 107: 1122-1129Abstract Full Text Full Text PDF PubMed Scopus (217) Google Scholar, Scott et al, 2013aScott R.T. Upham K.M. Forman E.J. Hong K.H. Scott K.L. Taylor D. Tao X. Treff N.R. Blastocyst biopsy with comprehensive chromosome screening and fresh embryo transfer significantly increases in vitro fertilization implantation and delivery rates: a randomized controlled trial.Fertil. Steril. 2013; 100: 697-703Abstract Full Text Full Text PDF PubMed Scopus (442) Google Scholar, Yang et al, 2012Yang Z. Liu J. Collins G.S. Salem S.A. Liu X. Lyle S.S. Peck A.C. Sills E.S. Salem R.D. Selection of single blastocysts for fresh transfer via standard morphology assessment alone and with array CGH for good prognosis IVF patients: results from a randomized pilot study.Mol. Cytogenet. 2012; 5: 24Crossref PubMed Scopus (240) Google Scholar). In addition, as we reported initially (Harton et al, 2013Harton G. Munné S. Surrey M. Grifo J. Kaplan B. Griffin D.K. Wells D. PGD Practitioners GroupDiminished effect of maternal age on implantation after Preimplantation Genetic Diagnosis with array comparative genomic hybridization.Fertil. Steril. 2013; 100: 1695-1703Abstract Full Text Full Text PDF PubMed Scopus (237) Google Scholar) and as is now also evident in the latest Society for Reproductive Technology (SART) data on implantation rates, cycles without preimplantation genetic testing (PGT) – the new terminology for PGS – show the typical decrease with age, while fresh transfer cycles with PGT show a lower decrease, and frozen cycles with PGT show no decrease at all (the difference between fresh and frozen being very interesting per se but the subject of another commentary). Miscarriages are also significantly reduced and therefore ongoing pregnancy rates per transfer increased. PGT, being a selection tool, does not improve cumulative pregnancy results. However, it does reduce time to pregnancy and pain and suffering resulting from miscarriages or affected babies. Dr Gleicher and colleagues are both too clever to be confused, and clever enough to cause confusion. Let us clarify (as opposed to confuse) some of their statements:■The ASRM Practice Committee from 2008 they mention comments on PGT-v1 (day 3 biopsy, FISH), a technique not used nowadays and not related to the issue of mosaicism at hand since mosaicism is not detectable on single blastomere biopsies.■‘Unacceptably high rates of false-positives’: PGT-v1 error rates have been widely published and the same has been done for PGT-v2 (Fiorentino et al, 2014Fiorentino F. Biricik A. Bono S. Spizzichino L. Cotroneo E. Cottone G. Kokocinski F. Michel C.E. Development and validation of a next-generation sequencing–based protocol for 24-chromosome aneuploidy screening of embryos.Fertil. Steril. 2014; 101: 1375-1382Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar, Kung et al, 2015Kung A. Munné S. Bankowski B. Coates A. Wells D. Validation of next-generation sequencing for comprehensive chromosome screening of embryos.Reprod. Biomed. Online. 2015; 31: 760-769Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar, Wells et al, 2014Wells D. Kaur K. Rico A. Grifo J. Anderson S. Sherlock J. Taylor J.C. Munné S. Clinical utilization of a rapid low-pass whole-genome sequencing technique for the diagnosis of aneuploidy in human embryos prior to implantation.J. Med. Genet. 2014; 51: 553-562Crossref PubMed Scopus (159) Google Scholar, Yang et al, 2015Yang Z. Lin J. Zhang J. Leng Fong W. Li P. Zhao R. Liu X. Podevin W. Kuang Y. Liu J. Randomized comparison of next-generation sequencing and array comparative genomic hybridization for preimplantation genetic screening: a pilot study.BMC Med. Genomics. 2015; 8 (Yang et al.): 30Crossref PubMed Scopus (55) Google Scholar). Unacceptable or acceptable is a personal decision between the patient and the physician. For PGT-v1, the error rate was higher and well known at about 10%, and stated clearly in reports and consents. For PGT-v2 using NGS technology and adding mosaicism screening, the error rate for classified euploid and fully aneuploid embryos is <1%. However, we now classify an intermediate group as mosaic, which has intermediate pregnancy potential (Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Friedenthal et al, 2018Friedenthal J. Maxwell S.M. Munné S. Kramer Y. McCulloh D.H. McCaffrey C. Grifo J.A. Next-generation sequencing for preimplantation genetic screening improves pregnancy outcomes compared to array comparative genomic hybridization in single thawed euploid embryo transfer cycles.Fertil. Steril. 2018; 109: 627-632Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar, Greco et al, 2015Greco E. Minasi M.G. Fiorentino F. Healthy babies after intrauterine transfer of mosaic aneuploid blastocysts.N. Engl. J. Med. 2015; 373: 2089-2090Crossref PubMed Scopus (345) Google Scholar, Grifo et al, 2015Grifo J. Colls P. Ribustello L. Escudero T. Liu E. Munne S. Why do array-CGH (aCGH) euploid embryos miscarry? Reanalysis by NGS reveals undetected abnormalities which would have prevented 56% of the miscarriages.Fertil. Steril. 2015; 104: e14Abstract Full Text Full Text PDF PubMed Google Scholar, Maxwell et al, 2016Maxwell S.M. Colls P. Hodes-Wertz B. McCulloh D.H. McCaffrey C. Wells D. Munné S. Grifo J.A. Why do euploid embryos miscarry? A case-control study comparing the rate of aneuploidy within presumed euploid embryos that resulted in miscarriage or live birth using next-generation sequencing.Fertil. Steril. 2016; 106: 1414-1419Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar, Munné et al, 2016Munné S. Grifo J. Wells D. Mosaicism: ‘survival of the fittest’ versus ‘no embryo left behind.Fertil. Steril. 2016; 105: 1146-1149Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar).■Embryos are graded morphologically based on their potential for implantation. What is wrong with NGS results offering a gradient? A gradient is always better than a black or white result with a 10% error rate. Now the black and white (euploid or aneuploid) sections of the gradient have close to 0% error rate.■There is no evidence that ‘large numbers of perfectly normal embryos with normal pregnancy potential’ have been discarded, beyond the mentioned error rate. The fact that the error rate for euploid and aneuploid has been now reduced to almost 0% using NGS should be a matter to rejoice, not the contrary. Gleicher and colleagues seem to promote the idea of proactively transferring fully aneuploid embryos. There is limited data available on that approach, but in a small series of 10 fully aneuploid embryo transfers only one implanted and died shortly after birth (Munné, unpublished data). Who is being irresponsible?■The authors mention increasing numbers of healthy newborns were reported following transfer of so-called ‘aneuploid’ embryos, but again the authors introduce confusion by mixing reports that used techniques that did not differentiate aneuploid from mosaic embryos with those that did. Mosaic embryos are not fully aneuploid embryos: these two terms should not be used interchangeably.■The upper and lower limits of the mosaic gradient are not arbitrary. On average, a blastocyst biopsy contains 5 cells; thus the technique can at most recognize 1/5 – 4/5 abnormal cells to classify the sample as mosaic. Obviously, this is an average, as sometimes there are fewer and sometimes more cells, and depending on the sample quality and cells biopsied the mosaicism detection could increase or decrease. The fact is, depending on the abnormal cell load there is evidence that the embryos will have different pregnancy potential (Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar). A 25% mosaic is closer to the potential of a euploid embryo, while a 75% is closer to the potential of an aneuploid embryo.■The authors complain that ‘the sensitivity limitations of a piece of laboratory equipment now officially determine embryo fate’ but the same occurs for any diagnostic test in medicine. For example, CAP/NYSDoH/ISO15189 requirements state that any assay needs a limit of detection and sensitivity.■A mathematical model can provide completely different results depending on the premises upon which it is structured. There are questionable premises in their model, such as the high number of cells in a blastocyst, which may invalidate such analysis. Irrespective of that, real-world data provides us with an error rate of close to 0% for PGT using NGS (Fiorentino et al, 2014Fiorentino F. Biricik A. Bono S. Spizzichino L. Cotroneo E. Cottone G. Kokocinski F. Michel C.E. Development and validation of a next-generation sequencing–based protocol for 24-chromosome aneuploidy screening of embryos.Fertil. Steril. 2014; 101: 1375-1382Abstract Full Text Full Text PDF PubMed Scopus (184) Google Scholar, Kung et al, 2015Kung A. Munné S. Bankowski B. Coates A. Wells D. Validation of next-generation sequencing for comprehensive chromosome screening of embryos.Reprod. Biomed. Online. 2015; 31: 760-769Abstract Full Text Full Text PDF PubMed Scopus (89) Google Scholar, Wells et al, 2014Wells D. Kaur K. Rico A. Grifo J. Anderson S. Sherlock J. Taylor J.C. Munné S. Clinical utilization of a rapid low-pass whole-genome sequencing technique for the diagnosis of aneuploidy in human embryos prior to implantation.J. Med. Genet. 2014; 51: 553-562Crossref PubMed Scopus (159) Google Scholar, Yang et al, 2015Yang Z. Lin J. Zhang J. Leng Fong W. Li P. Zhao R. Liu X. Podevin W. Kuang Y. Liu J. Randomized comparison of next-generation sequencing and array comparative genomic hybridization for preimplantation genetic screening: a pilot study.BMC Med. Genomics. 2015; 8 (Yang et al.): 30Crossref PubMed Scopus (55) Google Scholar), as well as very few false negatives. All of this effectively negates statements such as ‘The absurdity of this explanation was demonstrated in mathematical models which established that even 100% aneuploidy in a single 6-cell TEB could mathematically not establish high enough probability that such a finding would suggest aneuploidy for the whole trophectoderm’. From doubting mosaicism to doubting the existence of aneuploidy?■The paper by Calhaz-Jorge et al, 2017Bolton H. Graham S.J.L. Van der A N. Kumar P. Theunis K. Fernandez Gallardo E. Voet T. Zernicka-Goetz M. Mouse model of chromosome mosaicism reveals lineage-specific depletion of aneuploid cells and normal developmental potential.Nat Commun. 2016; 7: 11165https://doi.org/10.1038/ncomms11165Crossref PubMed Scopus (251) Google Scholar shows that abnormal cells in mice embryos are not clonally distributed but mostly distributed at random. More studies are needed to confirm that finding, but regardless of clonality or not, the fact is that embryos classified by NGS as purely aneuploid or euploid are more likely to be so than with other techniques. The grey zone of mosaic embryos needs to be further studied and segmented, but incipient evidence suggests that a higher load of abnormal cells results in lower pregnancy rates (Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar).■We question the 50–80% mosaicism rate quoted by the authors. Using FISH in large studies showed a rate of around 30% mosaicism in day 3 embryos (Colls et al, 2007Colls P. Escudero T. Zheng X. Lenzi M. Cinnioglu C. Cohen J. Munné S. Increased efficiency of preimplantation genetic diagnosis for infertility through reanalysis of dubious signals.Fertil. Steril. 2007; 88: 53-61Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar, Munné et al, 2007Munné S. Chen S. Colls P. Garrisi J. Zheng X. Cekleniak N. Lenzi M. Hughes P. Fischer J. Garrisi M. Tomkin G. Cohen J. Maternal age, morphology, development and chromosome abnormalities in over 6000 cleavage-stage embryos.Reprod. Biomed. Online. 2007; 14: 628-634Abstract Full Text PDF PubMed Scopus (221) Google Scholar), and around 20% in day 5 embryos using NGS (Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar). If an embryo is fully aneuploid for one chromosome (meiotic origin) and mosaic for another (mitotic origin), the embryo should be classified as fully aneuploid. Because of that, with advancing maternal age the rate of mosaicism seems to decrease since more embryos are classified as fully aneuploid, ranging from 23% in young patients to 12% in over 42-year olds.■By their logic, if mosaicism was in 50–80% of embryos and if that had no effect on embryo viability then it would be seen very widely pre/postnatally. However this is not the case after 40 years of chorionic villus sampling (CVS) and more recent non-invasive prenatal testing (NIPT) results, where mosaicism is seen at no more than 2% incidence. This is even before you look at the PGS data where mosaicism is clearly seen and can be correlated with lower live birth rates and higher miscarriage rates (Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar).■The authors ask why, if there is self-correction in mosaic mice embryos (Calhaz-Jorge et al, 2017Bolton H. Graham S.J.L. Van der A N. Kumar P. Theunis K. Fernandez Gallardo E. Voet T. Zernicka-Goetz M. Mouse model of chromosome mosaicism reveals lineage-specific depletion of aneuploid cells and normal developmental potential.Nat Commun. 2016; 7: 11165https://doi.org/10.1038/ncomms11165Crossref PubMed Scopus (251) Google Scholar), PGT has any validity? Again they try to confuse the reader by equating mosaicism with aneuploidy (in the Bolton paper fully aneuploid embryos did not implant!). The mechanism of self-correction in the Calhaz-Jorge et al, 2017Bolton H. Graham S.J.L. Van der A N. Kumar P. Theunis K. Fernandez Gallardo E. Voet T. Zernicka-Goetz M. Mouse model of chromosome mosaicism reveals lineage-specific depletion of aneuploid cells and normal developmental potential.Nat Commun. 2016; 7: 11165https://doi.org/10.1038/ncomms11165Crossref PubMed Scopus (251) Google Scholar paper is that euploid cells in mosaic mouse embryos divide faster than abnormal ones and eventually take over and/or that the abnormal ones, especially those created in the Bolton paper, are non-viable. Then, the more euploid cells an embryo has the higher is its chance to develop. But a fully aneuploid embryo cannot self-correct in this way because it has no euploid cells (as also illustrated by the Bolton paper). Thus, PGT has validity. Besides, this is a mouse model. Mice have 3% aneuploidy rates while humans have 40%. This paper might not be relevant to humans, regardless of whether or not it supports PGT.■In regard to the statistical analysis in the Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar paper, ROC curves were not considered by our statistician for several reasons. First, if we group the information according to the type of mosaic, a loss of information is produced mathematically and statistically, which is reflected in the ROC curves. In addition, the fact that the data are measured on a dichotomous scale also entails an unreliable interpretation of these curves. Additionally, the sample size is not suitable for the construction of these curves, and even less so if we group by type of mosaic. This would require estimating a distribution of information that also provides a posterior bias to the ROC curves. In short, and due to these facts, we consider that the contribution of the ROC curves in this study is not at all reliable and, on the contrary, we think that the logistic model proposed is the most suitable data analysis available for the study. In retrospect, this is now a moot point because adding the results of Fragouli et al, 2017Fragouli E. Alfarawati S. Spath K. Babariya D. Tarozzi N. Borini A. Wells D. Analysis of implantation and ongoing pregnancy rates following the transfer of mosaic diploid-aneuploid blastocysts.Hum. Genet. 2017; 136: 805-819Crossref PubMed Scopus (150) Google Scholar, Munné et al, 2017bMunné S. Blazek J. Large M. Martinez-Ortiz P.A. Nisson H. Liu E. Tarozzi N. Borini A. Becker A. Zhang J. Maxwell S. Grifo J. Babariya D. Wells D. Fragouli E. Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected by high resolution Next Generation Sequencing.Fertil. Steril. 2017; 108: 62-71Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar and Spinella et al, 2018Spinella F. Fiorentino F. Biricik A. Bono S. Ruberti A. Cotroneo E. Baldi M. Cursio E. Minasi M.G. Greco E. Extent of chromosomal mosaicism influences the clinical outcome of in vitro fertilization treatments.Fertil. Steril. 2018; 109: 77-83Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar clearly show a difference in ongoing pregnancy rates between mosaics with a high or low percentage of abnormal cells. If Dr Gleicher and colleagues want to take issue with PGT, for reasons of business, pleasure, or science, perhaps they should focus on blastocyst biopsy and not mosaicism. How is it possible that with 20–60% abnormality rates in egg donor blastocysts (Munné et al, 2017cMunné S. Alikani M. Ribustello L. Colls P. Martínez-Ortiz P.A. McCulloh D.H. Referring Physician Group*Euploidy rates in donor egg cycles significantly differ between fertility centers.Hum. Reprod. 2017; 32: 743-749Crossref PubMed Scopus (81) Google Scholar) there is no evidence (SART data, Munné et al, 2017aMunné S. Kaplan B. Frattarelli J. Gysler M. Child T. Nakhuda G. Shamma F.N. Silverberg K. Kalista T. Oliver K. Katz-Jaffe M. Wells D. Gordon T. Willman S. Global multicenter randomized controlled trial comparing single embryo transfer with embryo selection by preimplantation genetic screening using next-generation sequencing versus morphologic assessment.Fertil. Steril. 2017; 108 (O-43): e19Abstract Full Text Full Text PDF PubMed Google Scholar) of PGT benefiting younger patients? To us it seems that the blastocyst biopsy effect should be re-visited since there is no standardization and great variability between centers, Sub-optimal procedures may be causing damage which is only compensated at older ages when the selection potential of the technique is higher. While Dr Gleicher and colleagues are still shaking a fist at PGS v1, the field is moving towards v3, i.e. non-invasive PGS.