Fertility Topics Explained from the Experts at SFS
The numerical chromosomal configuration of a cell is referred to as its karyotype or ploidy. A cell with an irregular chromosome number is referred to as aneuploid while one with a normal karyotype, as euploid. It is predominantly (but not exclusively) the chromosomal configuration of the embryo that determines its subsequent ability, upon reaching a receptive uterine environment, to propagate a normal pregnancy, also referred to as its “competence.” A “euploid" (competent) embryo transferred to a receptive uterine environment (free of anatomical, or immunologic impediments to implantation is highly likely to propagate a “viable pregnancy “
Embryo transfer (ET) is undoubtedly one of the most important variables that determines IVF outcome. The procedure itself requires gentle placement of one or more embryo(s) near the roof of the uterine cavity under direct ultrasound guidance. Central to successful IVF outcome is the selection of high quality embryos for transfer to a receptive uterine environment, ones that are the most capable of propagating a normal pregnancy (i.e. “competent embryos”). The following methods for differentiating between “competent” and “incompetent” embryos have been in use:
Prior to PGT, the lack of a reliable method by which to accurately assess embryo “competence” often prompted even the most well intended IVF practitioner to transfer several embryos at a time in an attempt to optimize the likelihood of a pregnancy resulting. The widespread adoption of such practice, resulted in a virtual explosion in the incidence of high order multiple births (triplets or greater). The high costs associated with addressing short term and long term, obstetric, neonatal, and social complications resulting from such high order multiple pregnancies, is/was one of the main reasons why many health insurance providers in the U.S.A. were reluctant to voluntarily cover IVF services. The introduction of PGT into the clinical IVF arena by Levent Keskintepe and myself about 10 years ago, for the first time provided access to a method by which to relatively reliably differentiate between “competent” and “incompetent” embryos. This advance has led to:
Many IVF programs that offer PGT embryo selection, require that all participating patients consent to all aneuploid embryos () be disposed of. However, there is now growing evidence to suggest that following embryo transfer, some aneuploid embryos will in the process of ongoing development, convert to the euploid state (i.e. “autocorrection”) and then go on to develop into chromosomally normal offspring. So clearly, by summarily discarding all aneuploid embryos as a matter of routine we are sometimes destroying some embryos that might otherwise have “autocorrected” and gone on to develop into normal offspring. The basis for such embryo “autocorrection” lies in the fact that some embryos found through PGT-karyotyping to harbor one or more aneuploid cells (blastomeres) will often also harbor chromosomally normal (euploid) cells (blastomeres). The coexistence of both aneuploid and euploid cells coexisting in the same embryo is referred to as “mosaicism.” As stated, some mosaic embryos will In the process of subsequent cell replication convert to the normal euploid state (i.e. autocorrect). It is against this background, that an ever increasing number of IVF practitioners, rather than summarily discard PGT-identified aneuploid embryos are now choosing to cryobanking (freeze-store) certain of them, to leave open the possibility of ultimately transferring them to the uterus.
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