What to do with mosaic embryos
By Gorka Barrenetxea
Thanks to PGT-A (testing of embryos for aneuploidies) the chance of achieving an ongoing pregnancy per transfer has increased enormously. But, this is only true regarding the transfer of euploid embryos. Unfortunately, the selection of embryos means that in some cases no euploid embryos will be available for transfer. Furthermore, in other cases, a possible mosaicism will be the final genetic diagnosis. And the question is: what should we do with these embryos. Should they be considered abnormal (since they are not euploid) o could be regarded as “almost normal” embryos?
Actually, PGT-A assesses trophoectoderm (and no embryo cells) and sometimes there is no a correlation between a mosaicism in the external layer and the genetic burden of the embryo. Furthermore, in no few cases, the so called “possible mosaicism” reflects technical problems with the NGS (the usual procedure employed for the genetic analysis).
The available data in the literature allows the transfer of mosaic embryos once some conditions are fulfilled. Low level mosaic embryos (with a single aneuploidy) may be transferred. However, an invasive prenatal diagnostic procedure (amniocentesis) should be offered to the patient. Anyway, the possibility of having final reports different from euploid or aneuploid embryos, i.e. mosaicisms and/or non informative results must be known by patients before PGT-A is offered.