Study hypothesis: We hypothesized that a better discrimination between follicles containing oocytes with high developmental competence and those containing oocytes with low competence, based on a combination of a follicle's size and transcriptomic signature, will provide a reliable method to predict embryonic outcome of IVF.
Study finding: This study provides new insights on the impact of follicular size on oocyte quality as measured by embryonic development and demonstrates that medium follicles yield a better percentage of transferable embryos.
What is known already: Although it is generally accepted that large ovarian follicles contain better eggs, other studies report that a better follicular size subdivision and a better characterization are needed.
Study design, samples/materials, methods: Individual follicles (n = 136), from a total of 33 women undergoing IVF, were aspirated and categorized on the basis of their follicular liquid volume (small, medium or large) and the embryonic outcome of the enclosed oocyte: poor or good development. Comprehensive gene expression analysis between cells from the different sized follicles was performed using microarrays and quantitative RT-PCR to find molecular markers associated with follicular maturity and oocyte developmental competence.
Main results and the role of chance: The analysis of embryonic outcome in relation to follicular size indicates that the medium-sized follicles category yielded more transferable embryos (35%) compared with the largest follicles (30%) (NS). Gene expression analysis revealed expression markers with significant (P < 0.05) discrimination between the poor development groups for all three follicle sizes, and good development medium-size follicles, including up-regulation of thrombomodulin, transforming growth factor, beta receptor II and chondrolecti, and those associated with hyaluronan synthesis, coagulation and hepatocyte growth factor signalling.
Limitations, reasons for caution: These analyses were performed in a single cohort of patients coming from a single clinic and the biomarkers generated will require validation in different geographical and biological contexts to ensure their global applicability.
Wider implications of the findings: Medium-size follicles seem to be the optimal size for a positive embryonic outcome and are associated with competence markers that may help in understanding the ideal differentiation status during late folliculogenesis.
Large scale data: The data discussed in this publication have been deposited in The National Center for Biotechnology Information Gene Expression Omnibus database and are accessible through GEO Series accession number GSE52851.
Study funding and competing interests: This study was supported by Canadian Institutes of Health Research (CIHR) and Natural Sciences and Engineering Research Council of Canada (NSERC) to M.A.S. There are no competing interests to declare.
Keywords: follicular cells; follicular size; gene expression; granulosa cells; hepatocyte growth factor; oocyte competence.
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