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Embryo Quality: Selecting the Best Embryos to Transfer
by Geoffrey Sher, M.D. and Levent Keskintepe Ph.D.
“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 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, molecular 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 determine 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 that upon being transferred to a receptive uterine environment are capable of propagating a normal pregnancy (i.e. “competent embryos”).
The following methods currently in use for differentiating between “competent” and “incompetent” embryos all to a lesser or greater degree, lack both sensitivity and specificity in evaluating “embryo quality/”competence”: (1) Microscopic Embryo Grading which evaluates and grades embryos based upon their structural appearance (morphology). The Graduated Embryo Scoring (GES), was developed by SIRM lacks both sensitivity and specificity in evaluating “embryo competence” (2) Prolonged embryo culture to the Blastocyst stage, an approach aimed at culling the poorer quality embryos. Thus embryos that survive to the blastocysts stage are more likely than there GES high-scoring day-3 embryos, to be “competent”. (3) The Embryo Marker Expression Test (EMET) , introduced by Geoffrey Sher MD and Levent Keskintepe PhD in 2003 was the first prospective test to measure an embryo generated genetic “marker” as an improved method to evaluate “embryo competence”. 4) Preimplantation Genetic Diagnosis/Screening (PGD/S) with Fluorescence in-situ hybridization (FISH) of certain of the embryo’s chromosomes. However (FISH) only assesses 8-12 of 23 chromosome pairs and thus is not very helpful in measuring embryo “competence”. 5) Egg/embryo Competency Testing (ECT) promises to for the first time provide a highly discriminatory method for differentiating between “competent” and “incompetent” embryos. ECT could finally permit identification and the transfer of a single “competent” embryo. ECT with a great likelihood of a viable pregnancy resulting.