a finding. Alternatively, PGT technology allows genetic testing of human eggs and embryos before pregnancy is established, making it totally realistic to establish only HLA‐matched or potentially normal pregnancies without genetic predisposition to late‐onset disorders.
Notwithstanding the foregoing considerations, PGT has become an established clinical option in reproductive medicine and is applied using separate consent forms and research protocols approved by institutional ethics committees. Despite recent controversy regarding the quantitation of the impact of PGT‐A on clinical outcome, thousands of cases have been performed, resulting in the birth of thousands of healthy children born after PGT‐A. However, these protocols still require confirmatory CVS or amniocentesis and follow‐up monitoring of their safety and accuracy. Although PGT will help solve some of the longstanding ethical problems, such as the abortion issue (which could largely be avoided as a result of this approach), other issues could become a serious obstacle, particularly those related to “designer babies.” These considerations are highly relevant to the subject of PGT, as well as to any other new methods as we proceed with further development of appropriate technology for avoiding genetic disability.
Conclusion
Although the introduction of first‐trimester prenatal diagnosis by CVS has considerably improved the possibility of avoiding genetic diseases, selective abortion is an issue in the case of an affected fetus. PGT has been initiated to provide the option of avoiding the birth of an affected child without the need for abortion as an obligatory component in the prevention program. This chapter describes these important developments with the emphasis on addressing the problems of implementation of PGT into clinical practice.
Currently, PGT has been applied clinically for up to 600 different conditions, with thousands of unaffected children born after PGT performed for single‐gene and chromosomal disorders. Among the approaches to PGT introduced, blastocyst biopsy is now a standard. This became possible due to the progress in micromanipulation and biopsy and genetic analysis of single cells or small number of cells by PCR and currently by next‐generation technologies. The available experience has already demonstrated the practical utility of PGT, and the reliability and safety of this relatively new technology in assisted reproduction. The indications for PGT have been expanded beyond those used in prenatal diagnosis to include couples at high risk of having a child with a genetic disorder (in the face of antipathy toward elective abortion), poor‐prognosis IVF patients, couples at risk for producing offspring with late‐onset genetic disorders, and preimplantation HLA matching. Because of the high prevalence of chromosomal abnormalities in early pregnancy, the introduction of PGT‐A will not only make it possible to avoid the risk of age‐related aneuploidies, but will also considerably improve the embryo recovery and pregnancy outcome following PGT and should improve the effectiveness of IVF programs in general. Introduction of NGS‐based PGT‐A, which uses WGA as the first step of the technique, also makes it possible to perform PGT‐M with or without PGT‐HLA in the same biopsy material. Concomitant PGT‐A with PGT‐M, PGT‐SR, and PGT‐HLA are thus becoming standard procedures toward comprehensive PGT for genetic and chromosomal disorders.
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