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Designed to minimize chances of transferring genetically abnormal embryos, preimplantation genetic diagnosis (PGD) involvesin vitrofertilization (IVF), embryo biopsy, diagnosis and selective embryo transfer. Preimplantation genetic testing for aneuploidy (PGT-A) aims to avoid miscarriage and live born trisomic offspring and to improve IVF success. Diagnostic approaches include fluorescencein situhybridization (FISH) and more contemporary comprehensive chromosome screening (CCS) including array comparative genomic hybridization (aCGH), quantitative polymerase chain reaction (PCR), next-generation sequencing (NGS) and karyomapping. NGS has an improved dynamic range, and karyomapping can detect chromosomal and monogenic disorders simultaneously. Mosaicism (commonplace in human embryos) can arise by several mechanisms; those arising initially meiotically (but with a subsequent post-zygotic ‘trisomy rescue’ event) usually lead to adverse outcomes, whereas the extent to which mosaics that are initially chromosomally normal (but then arise purely post-zygotically) can lead to unaffected live births is uncertain. Polar body (PB) biopsy is the least common sampling method, having drawbacks including cost and inability to detect any paternal contribution. Historically, cleavage-stage (blastomere) biopsy has been the most popular; however, higher abnormality levels, mosaicism and potential for embryo damage have led to it being superseded by blastocyst (trophectoderm – TE) biopsy, which provides more cells for analysis. Improved biopsy, diagnosis and freeze-all strategies collectively have the potential to revolutionize PGT-A, and there is increasing evidence of their combined efficacy. Nonetheless, PGT-A continues to attract criticism, prompting questions of when we consider the evidence base sufficient to justify routine PGT-A? Basic biological research is essential to address unanswered questions concerning the chromosome complement of human embryos, and we thus entreat companies, governments and charities to fund more. This will benefit both IVF patients and prospective parents at risk of aneuploid offspring following natural conception. The aim of this review is to appraise the ‘state of the art’ in terms of PGT-A, including the controversial areas, and to suggest a practical ‘way forward’ in terms of future diagnosis and applied research.

Preimplantation genetic screening (PGS) involves the identification of chromosome abnormalities in IVF embryos (rather than targeting diagnosis to a specified gene). Chiefly employed for couples with advanced maternal age, recurrent miscarriage or recurrent IVF failure, it aims to improve IVF success, and reduce miscarriage and affected live birth rates. The process involves the sampling of cells by embryo biopsy, cytogenetic diagnosis, then selective transfer of an apparently chromosomally normal embryo in the hope of establishing a pregnancy. Although PGS is the most common variant of PGD (preimplantation genetic diagnosis), accounting for 80% of cases it has, from the outset, been one of the most controversial areas of reproductive medicine. The subject of intense debate, it attracts opinions ranging from recommendations that it should be applied in all IVF cases, through to the suggestion it should be discontinued completely. What do you think? Should it continue or not?

Introduction MtDNA copy number analysis remains controversial as a biomarker for embryo implantation and viability assessments with different authors reporting conflicting results. Initial reports ( Fragouli et al., 2015 , Diez-Juan et al., 2015 ) indicated that embryos with unusually high levels of mtDNA did not implant and those that did have a mean lower mtDNA count. Such findings have been challenged in different cohorts however ( Treff et al., 2017 , Victor et al., 2017 ). The purpose of this study was to determine if an association exists between mtDNA content and 3 clinical parameters: female age, the day of biopsy and implantation outcomes in euploid embryos in a large, blinded, cohort. Materials and Methods Aneuploidy testing was performed on 3971 blastocysts obtained from 1717 IVF/ICSI cycles in a single IVF unit, for patients with repeated implantation failures, recurrent miscarriages and/or advanced maternal age. Next generation sequencing (NGS) technology (Thermo Fisher) assessed chromosomal status. Euploid embryos were further analyzed by Ion Reporter software to identify mtDNA content by using the algorithm Mitoscore©. Blastocyst biopsy was performed by removing 4-8 trophectoderm cells, then blastocycsts were vitrified and transferred in a programmed thaw-cycle in the presence of euploid embryos. Embryos were divided by maternal age into “40 and over” and the remainder. Association between mtDNA and implantation was assessed in cycles where only one embryo was euploid so not to be affected by variables such as Mitoscore and/or morphology. Statistical analysis was performed by t-test (p Results 1866/3849 (48%) of embryos were euploid, with 681 cycles (39.6%) cancelled as none were diagnosed as such. Of 1838 where Mitoscores© were available, euploid embryos in the ≥40 age group (n=286) were more likely to have increased amounts of mtDNA copy number compared to younger group (n=1552)(P Conclusions In a previous preliminary study, we found no significant difference in mtDNA content between implanted vs. not-implanted embryos, however this may have been due to small sample size. After doubling patient number we now report a statistically significant difference (p=0.03) suggesting some value to Mitoscore in our hands. Nonetheless, outliers still exist as embryos with high Mitoscores still implanting, bringing into some doubt claims of a negative predictive value. This study has advantages over previous ones in that it is a large, blinded study that was performed in a single setting where results are less likely to have been confounded by variables such as stimulation protocols and laboratory conditions. Discrepant results may arise due to variability in data sets, different assessment protocols, software and algorithms. Further research on larger sample sizes in a prospective blind setting are needed in future.

Introduction PGT-A for translocations has been a valid approach in order to detect chromosomally normal/balanced embryos. While earlier studies utilized PGT-A for only rearranged chromosomes, comprehensive chromosomal analysis by array comparative genomic hybridization (aCGH) is nowadays the gold standard in PGT-A for translocation cases, allowing detection of a wide range of chromosomal abnormalities other than the ones involved in rearrangement -known as interchromosomal effect. Estimating the impact of interchromosomal effect based on the type of rearrangement can therefore greatly help the clinical management and may lead to the development of individual clinical strategies to maximize the outcome involving PGT-A approach at the blastocyst stage. This study is performed in order to analyze the presence as well as possible impact of interchromosomal effect in embryos of reciprocal and Robertsonian translocation carriers undergoing PGT-A for translocations. Material & Methods This retrospective study was conducted in Bahceci Fulya IVF Centre, between January 2014 and December 2017. It included a total of 128 PGT-A for translocations cycles performed for female and male reciprocal (n=87) and Robertsonian (n=41) translocation carriers. For all suitable embryos, a trophectoderm (TE) biopsy was performed on either on day 5 or day 6 and aCGH was used for comprehensive chromosomal screening (CCS) analysis. Patients and their embryos were grouped according to the nature of translocation as Group I (Reciprocal translocation carriers) and Group II (Robertsonian translocation carriers). Major laboratory as well as clinical parameters were compared between groups. Results Main patient & cycle parameters such as mean female age, number of previous ART trials, number of oocytes retrieved, fertilized, biopsied etc. were found to be similar in both groups (p>0.05). Results regarding embryo analysis and clinical outcome are shown in Table 1. Percent of embryos containing chromosomal abnormalities not involving rearranged chromosomes was significantly lover in embryos of reciprocal translocation carriers (Group I) whereas in the same group, the contribution of translocated chromosomes in overall aneuploidy was found to be significantly higher. Table 1: Embryo analysis and clinical outcome between groups. Group I Group II p Num. of cycles (n) 87 41 Embryos biopsied (n) 315 145 Embryos processed for analysis (n) 307 137 Embryos diagnosed (n, %) 304 (99.0) 135 (98.5) NS Normal embryos (n, %) 77 (25.3) 50 (37.0) NS Abnormal embryos (n, %) 227(74.7) 85 (63.0) NS Aneuploid/balanced embryos (n, %) 73 (24.0) 58 (43.0) p=0.0061 Euploid/unbalanced embryos (n, %) 100 (32.9) 14 (10.4) P Num. of cycles cancelled prior to ET (n) 39 (44.8) 13 (31.7) NS Num. of ET cycles (n) 40 31 Pregnancy rate (b-hCG+, n, %) 31 (77.5) 20 (64.5) NS Clinical pregnancy rate (Sac+, n, %) 29 (72.5) 17 (54.8) NS Live birth/Ongoing (%) 22 (55.0) 13 (41.9) NS Missed abortus (%) 6 (15.0) 4 (12.9) NS Conclusions Our data and results have shown that, although they generate acceptable clinical pregnancies, embryos of Robertsonian translocation carriers have increased aneuploidies for chromosomes not involved in the translocation. This result indicates that besides cleavage stage, interchromosomal effect can significantly contribute the genetic status of human embryos at the blastocyst stage, leading to poorer clinical outcome.