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PGD for aneuploidy and translocation chromosome imbalance by cleavage stage biopsy

PGD for aneuploidy and translocation chromosome imbalance by cleavage stage biopsy

 

Francesco Fiorentino

 

“GENOMA”- Molecular Genetics Laboratory, Via di Castel Giubileo, 11 00138 Rome – Italy

 

Embryo assessment is a crucial component to the success of in vitro fertilization (IVF). Conventional embryo selection methodologies, based on morphological criteria, are not sufficient.  In fact, many women fail to achieve a pregnancy even after transfer of good quality embryos.  These couples may undergo multiple unsuccessful IVF cycles and so often seek further options to improve their chances of a positive outcome.

The evidence that a high rate of embryos produced in vitro present chromosomal abnormalities, and thus have reduced potential for achieving a viable pregnancy, has suggested the use of preimplantation genetic diagnosis for aneuploidy screening (PGS) in order to improve IVF outcomes. Data from comprehensive aneuploidy screening of embryos by array comparative genomic hybridization (Array-CGH) demonstrated that aneuploidies may occur in any of the 24 chromosomes, indicating that aneuploidy screening of all chromosomes is necessary to determine whether an embryo is chromosomally normal.

Array-CGH is now used extensively worldwide, not only for whole chromosome aneuploidy screening but also for preimplantation genetic diagnosis (PGD) of segmental chromosome imbalance in couples carrying balanced reciprocal or Robertsonian translocations. Initial reports on clinical application of this technology have documented improved pregnancy outcomes following transfer of screened embryos. However, the optimal stage of preimplantation development at which PGS/PGD should be performed still remains to be determined.

Although clinical results have been promising, further evidences are required to establish whether PGS results in enhanced live birth rate, and if this is the case, to identify which patients may benefit from the procedure. The results from several ongoing randomized controlled trials, performed at different cell biopsy stage and categories of patients, will provide the data needed to accept or reject the clinical efficacy of PGS.