**1. Introduction**

Endometriosis is a frequent disease in reproductive-age women [1], consisting of the presence of endometrial tissue outside the uterine cavity. Endometriosis is frequently associated with infertility, being present in 25–50% of infertile patients [2]. On the other hand, 30–50% of endometriosis patients report difficulties to become pregnant [2]. In a large cohort study, women with endometriosis younger than 35 years old had a two-fold higher risk of infertility in comparison with women without endometriosis [3]. The mechanisms underlying the association between endometriosis and infertility are incompletely clarified, with both anatomical and microenvironmental disturbances being suggested [4]. While in infertile patients with advanced-stage endometriosis anatomical changes might be involved (peritubal and periovarian adhesions), the presence of infertility in milder forms of endometriosis suggests other mechanisms. Thus, decreased ovarian reserve, altered folliculogenesis, oocyte quality and endometrial receptivity were reported as possible contributors to infertility [4].

The extent and severity of endometriosis lesions are variable, ranging from few implants on the pelvic peritoneum to surrounding organs infiltration or extension outside the pelvis. Several grading systems for endometriosis have been created, but their predictive value for fertility is unclear. One of these classification systems, the Endometriosis Fertility Index (EFI) which is based on the scores from the American Society for Reproductive Medicine (ASRM) system [5] combined with anamnestic and information from surgery, gives a score from 0 to 10 points [6]. It was shown that a score between 0 and 3 is associated with a 10% probability of obtaining pregnancy after 3 years with non-IVF treatments, while a score of 9–10 points is associated with a 75% chance of pregnancy [6, 7]. The predictive value of the EFI score for pregnancy was also confirmed for IVF treatments [8].

The impact of variate treatments for endometriosis on chances to obtain pregnancy and the efficacy of infertility treatments is still a matter of discussion. Thus, whether surgery contributes to the improvement of fertility in endometriosis or is preferable to perform infertility treatments needs further clarification.

In minimal or mild endometriosis without anatomical disruption, it was shown that laparoscopic removal of endometriosis implants improves fertility with an increase of risk ratio of 1.44 [9] and an odds ratio of 1.94 [10]. In a large Canadian multicenter study, the monthly fecundity rate and the 36-week cumulative probability of pregnancy increased from 2.4 to 17.7% for a diagnostic laparoscopy to 4.7 and 30.7% for laparoscopic surgery [11]. However, these rates of pregnancy should be discussed with the patients in the light of similar success rates of 30% after only one cycle of IVF taking into account the age, ovarian reserve or the cost of the treatment [12].

In patients with moderate and severe endometriosis surgery aims to remove large endometriomas and to restore the pelvic anatomy. Data regarding the effect of surgery on fertility in this category of patients are lacking. Excision of endometrioma is controversial in infertile patients taking into account the risk to decrease the ovarian reserve and lack of evidence of benefits on IVF outcome [13].

IVF could be a treatment option for infertility in patients with endometriosis. Therefore, the performance of patients with endometriosis at IVF and their predictors should be clarified to elaborate strategies for ovarian stimulation and to improve IVF outcomes. Oocyte yield at IVF is an important predictor of live birth in the general population of patients performing IVF, but it might be affected by the microenvironmental changes associated with endometriosis. Moreover, the AMH production could be disturbed in endometriosis, possibly interfering with its relationship with the ovarian reserve.

Therefore, the present paper aims to review the literature regarding the association of endometriosis with oocytes number and serum AMH level in infertile patients performing IVF, and the predictive value of AMH for the response to controlled ovarian stimulation.
