BACKGROUND Preimplantation genetic testing (PGT) encompasses methods that allow embryos to be tested for severe inherited conditions or for chromosome abnormalities, relevant to embryo health and viability. In order to obtain embryonic genetic material for analysis, a biopsy is required, involving the removal of one or more cells. This invasive procedure greatly increases the costs of PGT and there have been concerns that embryo viability could be compromised in some cases. The recent discovery of DNA within the blastocoele fluid (BF) of blastocysts and in spent embryo culture media (SCM) has led to interest in the development of non-invasive methods of PGT (niPGT). OBJECTIVE AND RATIONALE This review evaluates the current scientific evidence regarding non-invasive genetic assessment of preimplantation embryos. The success of different PGT methodologies in collecting and analysing extra-embryonic DNA is evaluated, and consideration is given to the potential biological and technical hindrances to obtaining a reliable clinical diagnosis. SEARCH METHODS Original research and review papers concerning niPGT were sourced by searching PubMed and Google Scholar databases until July 2019. Searches comprised the keywords: 'non-invasive'; 'cell-free DNA'; 'blastocentesis'; 'blastocoel fluid'; 'spent culture media'; 'embryo culture medium'; 'preimplantation genetic testing'; 'preimplantation genetic diagnosis'; 'preimplantation genetic screening'; and 'aneuploidy'. OUTCOMES Embryonic DNA is frequently detectable in BF and SCM of embryos produced during IVF treatment. Initial studies have achieved some success when performing cytogenetic and molecular genetic analysis. However, in many cases, the efficiency has been restricted by technical complications associated with the low quantity and quality of the DNA. Reported levels of ploidy agreement between SCM/BF samples and biopsied embryonic cells vary widely. In some cases, a discrepancy with respect to cytogenetic data obtained after trophectoderm biopsy may be attributable to embryonic mosaicism or DNA contamination (usually of maternal origin). Some research indicates that aneuploid cells are preferentially eliminated from the embryo, suggesting that their DNA might be over-represented in SCM and BF samples; this hypothesis requires further investigation. WIDER IMPLICATIONS Available data suggest that BF and SCM samples frequently provide DNA templates suitable for genetic analyses, offering a potential means of PGT that is less expensive than traditional methods, requires less micromanipulation skill and poses a lower risk to embryos. Critically, DNA isolation and amplification protocols must be optimised to reproducibly obtain an accurate clinical diagnosis, whilst minimising the impact of confounding factors such as contamination. Further investigations are required to understand the mechanisms underlying the release of embryonic DNA and to determine the extent to which this material reflects the true genetic status of the corresponding embryo. Currently, the clinic al potential of niPGT remains unknown.

中文翻译：

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无创植入前基因检测（niPGT）：生殖遗传学的下一场革命？

背景技术植入前基因测试（PGT）涵盖了允许对胚胎进行严格遗传条件或染色体异常测试的方法，这些条件与胚胎健康和生存能力有关。为了获得用于分析的胚胎遗传材料，需要进行活检，包括去除一个或多个细胞。这种侵入性方法极大地增加了PGT的成本，并且人们担心在某些情况下可能损害胚胎的生存能力。囊胚的囊胚腔液（BF）和用过的胚胎培养基（SCM）中最近发现的DNA引起了人们对PGT（niPGT）非侵入性方法发展的兴趣。目的和理由本评价评估有关植入前胚胎无创遗传评估的当前科学证据。评估了不同PGT方法在收集和分析胚外DNA方面的成功，并考虑了获得可靠临床诊断的潜在生物学和技术障碍。搜索方法有关niPGT的原始研究和评论论文都是通过搜索PubMed和Google Scholar数据库直至2019年7月而获得的。'无细胞DNA'；'blastocentesis'; “囊胚液”；“用过的文化媒体”；“胚胎培养基”；'植入前基因检测'；'植入前遗传学诊断'；“植入前基因筛查”；和“非整倍性”。结果胚胎DNA经常在IVF治疗期间产生的胚胎的BF和SCM中检测到。进行细胞遗传学和分子遗传学分析时，初步研究已获得一些成功。但是，在许多情况下，效率受到与DNA数量少和质量低有关的技术复杂性的限制。报道的SCM / BF样品和活检的胚胎细胞之间的倍性一致性水平差异很大。在某些情况下，在滋养外生组织活检后获得的细胞遗传学数据方面的差异可能归因于胚胎镶嵌或DNA污染（通常来自母体）。一些研究表明，非整倍体细胞优先从胚胎中清除，这表明它们的DNA在SCM和BF样品中可能过高。这个假设需要进一步研究。潜在影响BF和SCM样品经常提供适用于遗传分析的DNA模板，提供了一种潜在的PGT手段，该手段比传统方法便宜，需要较少的显微操作技能，并且对胚胎的风险较低。至关重要的是，必须对DNA分离和扩增方案进行优化，以可重复获得准确的临床诊断，同时最大程度地减少混杂因素（如污染）的影响。需要进一步的研究，以了解释放胚胎DNA的潜在机制，并确定这种材料在多大程度上反映了相应胚胎的真实遗传状态。目前，niPGT的临床潜力仍然未知。提供一种比传统方法便宜的潜在PGT手段，需要较少的显微操作技能，并且对胚胎的风险较低。至关重要的是，必须对DNA分离和扩增方案进行优化，以可重复获得准确的临床诊断，同时最大程度地减少混杂因素（如污染）的影响。需要进一步的研究，以了解释放胚胎DNA的潜在机制，并确定这种材料在多大程度上反映了相应胚胎的真实遗传状态。目前，niPGT的临床潜力仍然未知。提供一种比传统方法便宜的潜在PGT手段，需要较少的显微操作技能，并且对胚胎的风险较低。至关重要的是，必须对DNA分离和扩增方案进行优化，以可重复获得准确的临床诊断，同时最大程度地减少混杂因素（如污染）的影响。需要进一步的研究，以了解释放胚胎DNA的潜在机制，并确定这种材料在多大程度上反映了相应胚胎的真实遗传状态。目前，niPGT的临床潜力仍然未知。同时将混杂因素（如污染）的影响降到最低。需要进一步的研究，以了解释放胚胎DNA的潜在机制，并确定这种材料在多大程度上反映了相应胚胎的真实遗传状态。目前，niPGT的临床潜力仍然未知。同时将混杂因素（如污染）的影响降到最低。需要进一步的研究，以了解释放胚胎DNA的潜在机制，并确定这种材料在多大程度上反映了相应胚胎的真实遗传状态。目前，niPGT的临床潜力仍然未知。