Embryo quality is the ability of an embryo to perform successfully either or both in terms of conferring a high pregnancy rate or/and resulting in a healthy person. Embryo profiling is the estimation of embryo quality by qualification and/or quantification of various parameters. Estimations of embryo quality guides the choice in embryo selection in in vitro fertilization.
Prediction of pregnancy rates
Time-lapse microscopy is an expansion of microscopy wherein the morphology of embryos is studies over time. A review in 2014 considered its evidence to be lacking, and that it should thereforeremain an experimental strategy subject to institutional review and approval. Studies using the EmbryoScope(tm) time-lapse incubator have used several indicators for embryo quality, such as direct cleavage from 1 to 3 cells, as well as the initiation of compaction and start of blastulation. Also, two-pronuclear zygotes (2PN) transitioning through 1PN or 3PN states tend to develop into poorer-quality embryos than those that constantly remain 2PN.
Also, methods are emerging in making comprehensive analyses of up to entire genomes, transcriptomes, proteomes and metabolomes which may be used to score embryos by comparing the patterns with ones that have previously been found among embryos in successful versus unsuccessful pregnancies:
- In transcriptome evaluation, however, gene expression profiling studies of human embryos are limited due to legal and ethical issues. An alternative or complement is gene expression profiling of cumulus cells surrounding the oocyte and early embryo, or on granulosa cells. Profiling of cumulus cells can give valuable information regarding the efficiency of an ovarian hyperstimulation protocol, and may indirectly predict oocyte aneuploidy, embryo development and pregnancy outcomes, without having to perform any invasive procedure directly in the embryo.
- Proteome profiling of embryos can indirectly be evaluated by sampling of proteins found in the vicinity of embryos, thereby providing a non-invasive method of embryo profiling. Examples of protein markers evaluated in such profiling include CXCL13 and granulocyte-macrophage colony-stimulating factor, where lower protein amounts are associated with higher implantation rates.
Another level of opportunity can be achieved by having the evaluation of the embryo profile tailored to the maternal status in regard to, for example health or immune status, potentially further detailed by similar profiling of the maternal genome, transcriptome, proteome and metabolome. Two examples of proteins that may be included in maternal profiling are endometrium-derived stathmin 1 and annexin A2, whose down- and up-regulation, respectively, are associated with higher rates of successful implantation.
The main method currently used to predict the health of a resultant person of an embryo is preimplantation genetic diagnosis (also called preimplantation genetic screening, preimplantation genetic profiling or PGP), in order to determine whether the resultant person will inherit a specific disease or not. On the other hand, a systematic review and meta-analysis of existing randomized controlled trials came to the result that there is no evidence of a beneficial effect of PGP as measured by live birth rate. On the contrary, for women of advanced maternal age, PGP significantly lowers the live birth rate. Technical drawbacks, such as the invasiveness of the biopsy, and chromosomal mosaicism are the major underlying factors for inefficacy of PGP.
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