Since the recognition of the role endometriosis may have on reproductive function there have been proposed two potential mechanisms to account for this. The first mechanism looks at the effect of endometriosis on the quality of oocytes, whereas the second deals with the impact that endometriosis may have on the uterus and the endometrium. 

Various studies have looked at the degree to which both factors affect fertility and, so far, it appears that endometriosis has primarily an adverse effect on the quality of oocytes. This is suggested by studies based on the oocyte donation model, where endometriosis can be controlled by selecting the donor’s as well as the recipient’s profile with regards to the presence of endometriosis.

When looked under the microscope, oocytes from women with endometriosis have more frequently morphological defects, especially extra-cytoplasmic defects, as in their zone pellucida, the peri-vitelline space, as well an increased incidence of abnormal shape. In addition to this, when researchers looked at the mitochondrial mean DNA copy number in oocytes from women with endometriosis, they found that there was a reduction in oocytes of women with endometriosis, suggesting a decreased oocyte quality as a result of impaired mitochondrial structure and function. 

Another piece of evidence for the negative impact endometriosis has on oocyte quality came from IVM studies in mouse oocytes matured in peritoneal fluid from patients with endometriosis. Both microtubule abnormalities, as well as chromosome alterations were increasing with advancing degrees of severity of endometriosis.

Although oocyte quality can be adversely affected by the presence of endometriosis through the above mechanisms, the quality of embryos that women with endometriosis produce in vitro has shown conflicting data. So far, it is not clear whether embryo quality is any different as judged by morphology in the microscope, however, studies have suggested that not only morphokinetic differences may exist, but according to some researches aneuploidy rates may be increased. The conflicting data with regards to endometriosis impact on embryo quality, if anything, highlights the importance of methodology in research, the diagnostic criteria for endometriosis and the definition of severity of disease, as well appropriate selection of control patients.

©2021, Nicholas Christoforidis, Fertility Matters
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