Preimplantation genetic screening: definition, role in IVF, evolution and future perspectives

Mini-review, 56 – 64
doi: 10.11138/cce/2015.2.2.056
Prenatal Genetic Screening (PGS) is a diagnostic technique used in assisted reproductive technologies (ART) in order to detect chromosomal aneuploidies in embryos obtained through in vitro fertilization (IVF). Aneuploidy is the main cause of preimplantation failure and pregnancy loss inwomen. The main goal of PGS strategy is to identify euploid embryos and prevent the abnormal ones from being transferred, thus increasing the efficiency of IVF treatment, in terms of higher implantation rate and lower miscarriage rate per transfer. PGS at blastocyst stage offers different advantages over PGS on polar body (PB) or single blastomere: a higher amount of starting material and a more robust genetic analysis, a minor impact of mosaicism, a lower impact of the biopsy on embryo vitality, development and implantation potential as well as optimization of laboratory workload and procedural costs. At present, three randomized controlled studies have been published showing a consistently higher implantation rate and lower miscarriage rate when euploid blastocysts were transferred compared to untested embryos. Accordingly, blastocyst stage
PGS can be considered a validated method to enhance embryo selection in IVF. However, even when transferring a euploid embryo with excellent morphology, still 40-50% of these embryos fail to implant or produce a delivery. Blastocyst morphology and developmental timings, as well as morphokinetic do not seem to be good indicator to further enhance selection between euploid blastocysts. Thus, the attention must be turned to other criteria, in order to identify additional biomarkers of reproductive potential of euploid blastocysts. The purpose of this review is to give a full explanation of PGS technique, its advantages over conventional embryo selection and to define the next steps towards for the discovery of additional criteria to further enhance embryo selection that could be used together with aneuploidy screening.
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