Endometriosis and infertility.

Endometriosis remains a very enigmatic and perplexing disease. The exact mechanism by which endometriosis causes infertility is still unclear. In the present paper, we will review possible mechanisms leading to subfertility or infertility in women with endometriosis and examine them according to location. Endometriosis in the pelvic cavity is a pathology associated with a general inflammatory response and should therefore be considered an inflammatory disease. Inflammatory changes affect the peritoneal fluid and hence the intratubal milieu, since the ampulla (where fertilization takes place) is exposed to peritoneal fluid through the fimbria. Any inflammatory change at this level may therefore impact fertilization and natural conception. The relationship between ovarian endometriomas and infertility may, of course, be explained by the presence of periovarian endometriosis. In the ovary, fibrosis observed in some cortical areas is induced by the inflammatory reaction caused by the presence of endometriomas. The association between fibrosis and a reduced ovarian reserve was demonstrated. Upregulated recruitment and the subsequent demise of early follicles may result in focal exhaustion of primordial follicles. Burn-out of early follicles by a local pelvic inflammatory environment caused by endometriomas may therefore be suggested. However, intraovarian inflammation, subsequent fibrosis and depletion of the ovarian reserve constitute another reason that should also be given due consideration. In addition, surgery should not be ruled out as a possible cause of ovarian reserve depletion. In conclusion, potential mechanisms leading to infertility are numerous, and while some of them remain hypothetical for now, others are supported by clear evidence. These possible mechanisms were reviewed in the present paper.