**3. The association between endometriosis and oocyte yield in infertile patients performing IVF**

The relationship between endometriosis and oocytes yields in infertile patients performing IVF was previously studied, but the results are divergent. Senapati et al. found that patients with endometriosis obtain fewer oocytes in comparison with patients with other causes of infertility undergoing IVF in a big database of

347,185 assisted reproductive technic cycles [28]. In this study, the presence of endometriosis was associated with a lower number of oocytes in patients with isolated endometriosis or association with other causes of infertility, including diminished ovarian reserve [28]. The negative association between endometriosis and oocytes yield was also studied by a meta-analysis that included 20,167 patients with endometriosis and 121,931 without endometriosis [29]. Subgroups with 1703 women with stage III/IV endometriosis were compared with 2227 women with stage I/II endometriosis. Although, a small difference in oocytes yield was observed in favor of non-endometriosis patients, the authors concluded that the quality of the evidence is very low, not allowing meaningful conclusions to be drawn [29]. No significant difference in patients with variate stages of endometriosis was reported [29]. Moreover, in both studies patients with and without previous surgery for endometriosis were included, generating a possible bias [28, 29]. Thus, Dong et al. analyzed only patients with previous surgery for endometriosis and found that patients with stage III/IV endometriosis obtained lower oocytes number in comparison with controls [30], suggesting that surgery for severe endometriosis might negatively affect COS response. Several other studies confirmed the negative association between surgery for endometriosis and oocytes yield in women with advanced-stage endometriosis [31]. In patients operated for endometrioma, laparoscopic cystectomy is associated with decreased oocytes number, with an additional effect of bilateral versus unilateral cystectomy [32]. Similarly, bilateral surgery for endometrioma was shown to decrease the oocytes number in comparison with unoperated patients [33].

Regarding the association of variate types of endometriosis with COS response, a recent meta-analysis found that unoperated endometriomas are associated with reduced oocytes number in IVF cycles [34]. Papaleo et al. found that profound infiltrative endometriosis has an additional negative effect on oocytes yield in comparison with patients with isolated ovarian endometrioma, supporting the hypothesis that variate types of endometriosis lesions can differently impact the ovarian response [35]. In turn, a small study that included only patients with stage I and II endometriosis found similar oocytes number with patients performing IVF for tubal infertility [15].
