Objective: To identify associations between presence of endometriosis and oocyte defects, embryo developmental potential, and cycle outcomes. Methods: This study looked into the impact of endometriosis on oocyte and embryo quality, and blastocyst formation probability. Endometriosis was also correlated with cycle characteristics. In order to avoid age-related bias, in the first analysis only patients aged 36 years or younger were included, and the cycles were split into endometriosis

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... cycles (n=431; 3172 oocytes) and other cycles (n=2510; 24480 oocytes). Results: The number of retrieved oocytes (10.6±21.2 vs. 14.6±21.1, P<0.001), oocyte yield (68.1±20.0% vs. 70.6±19.6%, P=0.015), and embryos obtained (6.1±4.43 vs. 7.8±5.12, P<0.001) were lower among patients with endometriosis. Implantation rates (28.1%±38.9% vs. 33.9±42.7, P<0.001) were lower among patients with endometriosis, but fertilization, pregnancy, miscarriage and cycle cancelation rates were not different. There was a significant increase in the incidence of extra-cytoplasmic, but not intra-cytoplasmic, oocyte defects among patients with endometriosis. The quality of embryos (45.3% vs. 47.3%, P=0.037) collected from patients with endometriosis was lower, but blastocyst formation rates were unaltered. Conclusions: A possible explanation for the lower implantation rates seen in patients with endometriosis is the poorer quality of the oocytes and embryos observed in this group of patients.