Inverted microscopy as a high performance tool for pre denudation evaluation of oocyte nuclear maturity.

Objective: We aimed to show that inverted microscope is a reliable and highly accurate method for evaluating oocyte nuclear maturation before cumulus-oocyte complex (COC) denudation. Materials and Methods: This single-center prospective observational study was conducted between 15 October and 15 November 2025. Non-dominant follicles with a diameter <10 mm were retrieved and evaluated under an inverted microscope to predict oocyte nuclear maturation prior to COC denudation. A total of 974 oocytes were retrieved from 59 patients; 250 COCs obtained from follicles <10 mm were analyzed. COCs were divided into three groups: (i) COCs with germinal vesicle (GV) oocytes, (ii) COCs with non-GV oocytes, and (iii) unclassified COCs. Two hours later, COCs were denuded, and the diagnostic accuracy of the inverted microscope was assessed. Results: Ninety-seven COCs were classified as GV, 127 as non-GV, and 26 as unidentified. After denudation, 94 of 97 COCs were confirmed as GV oocytes, and 124 of 127 COCs were confirmed as non-GV oocytes. The accuracy of the inverted microscope in identifying nuclear maturation for GV and non-GV oocytes was 96.91% and 97.64%, respectively. No statistically significant difference in diagnostic accuracy was observed between embryologists. Conclusion: Currently, no method can definitively determine oocyte nuclear maturation before COC denudation. This method allows the prediction of oocyte nuclear maturation before denudation with high accuracy, potentially improving in vitro maturation outcomes by preserving cumulus-oocyte communication.