Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 75

Although there is no evidence of the detrimental effect of biopsy procedures on embryo viability, the potential for damage cannot be excluded, so the development of noninvasive preimplantation genetic testing (NIPGT) is of increasing importance. The fact that DNA fragments of approximately 150 bp are present in cell‐free DNA of blastocoele fluid and spent culture medium, is the basis of the concept that NIPGT can be developed analogous to noninvasive prenatal testing (NIPT), because these DNA may originate from breakdown of nuclear DNA derived from cells damaged at biopsy or undergoing apoptosis during cell division. Available reports suggest that the technique may in future be applicable for preselection of euploid embryos for transfer.^49–58 Although the usefulness of blastocoele fluid for PGT by different groups lacks consensus, its use has been proposed to identify at‐risk embryos from younger patients who otherwise have no accessible indication for PGT‐A.^{49, 50} The other approach, based on the use of cell‐free DNA in culture media, represents the genuine noninvasive approach analogous to monitoring cell‐free DNA in maternal plasma during pregnancy,^51–58 with the concordance studies showing progress. In one of these studies, the test was offered to infertility patients presenting for PGT‐A in the format of a clinical trial. Enough DNA for testing was detected in 88% of cases, with 80% concordance to biopsy results.⁵⁵ In another prospective study, blastocoele samples and spent culture medium samples were compared to diagnostic biopsy samples that were processed for PGT‐M and PGT‐A. Overall results demonstrated that neither blastocoele samples nor spent medium were sufficiently robust approaches for aneuploidy or single‐gene disorders and cannot be applied clinically until the risk of maternal contamination can be excluded. This risk is particularly high in spent culture medium samples due to maternal cumulus DNA contamination.⁵⁶ In the other study DNA in spent medium was shown to be detectable on day 3, but more reproducibly on day 5, with concordances of 65 and 70 percent with biopsy samples, which are not high enough for practical application.⁵⁷

Although the origin of the DNA in spent culture medium is not clear, it was postulated that results of the test may have a prognostic utility and better prediction of reproductive outcome if euploid embryos with euploid spent media results are transferred. This is in contrast to the euploid embryo transfer outcome with spent media showing imbalanced results.⁵⁸ This is also in agreement with the blastocoele data, which suggested a significantly improved embryo transfer outcome for those euploid embryos whose blastocoele fluid has a higher quantity of DNA based on WGA.⁵⁰ Thus, clearly more research is needed to validate the usefulness of spent culture medium and blastocoele fluid for PGT.