Affected Ovary Relative Volume: A Novel Sonographic Predictor of Ovarian Reserve in Patients with Unilateral Endometrioma—A Pilot Study

Background: The assessment of ovarian reserve in the case of endometrioma is of pivotal importance for planning a tailored management. However, both the antral follicle count (AFC) and the antimüllerian hormone (AMH) dosage are subject to a fair degree of variability in ovarian endometriosis. This study aimed to identify a sonographic parameter of ovarian reserve that could implement current available markers in patients with unilateral endometrioma. Methods: Patients with unilateral endometrioma admitted to our Endometriosis Center between March 2018 and April 2019 were enrolled. Transvaginal ultrasonography for the evaluation of eight sonographic indicators and AMH level determination were performed. The relationship between AMH level and each indicator was assessed. Results: Thirty-four women were included. There was a positive significant correlation between AMH level and the healthy ovary AFC (HO-AFC) (r = 0.36 p = 0.034). A stronger, negative correlation between AMH level and the ratio between the volume of the affected and the healthy ovary (affected ovary relative volume, AORV) (r = −0.47; p = 0.005) was evidenced. AORV had a satisfactory accuracy (AUC 0.73; CI 0.61–0.90; p = 0.0008), and the cut-off value of 5.96 had the best balance of sensitivity/specificity in distinguishing between patients with a good ovarian reserve (AMH ≥ 2 ng/mL) and those at risk of ovarian reserve depletion after excisional surgery. Conclusion: AORV may be a useful tool to assess ovarian reserve in patients with unilateral endometrioma without previous surgery and to guide physicians in clinical management.