Epigenetic Influences on Oocyte Developmental Competence: Perifollicular Vascularity and Intrafollicular Oxygen

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Abstract
Purpose: Studies indicating that the developmental competence of the human oocyte is influenced by the level of intrafollicular oxygen are described. Methods: Perifollicular vascularity and dissolved oxygen content were determined by color Doppler ultrasonography and analysis of follicular fluid at ovum retrieval, respectively, in stimulated cycles for in vitro fertilization. Results: Differences in the degree of perifollicular vascularity correlate with differences in the dissolved oxygen content of the corresponding follicular fluid. Oocytes with cytoplasmic and chromosomal disorders and embryos with multinucleated blastomeres and limited developmental ability were derived predominantly from underoxygenated follicles. Findings from several studies indicate that embryos with the highest implantation potential originate from follicles that are well-vascularized and oxygenated. Conclusions: Follicular vascularity and oxygen content appear to be important determinants of oocyte competence. Possible causes of differences in follicle-specific vascularity and the potential effects of severe hypoxia on the normality of molecular and cellular processes during follicle growth and preovulatory development are discussed.