The Ovary: An Asymmetric Gonad?

1.1. Study Question Does functional asymmetry exist between the right and left human ovary in terms of oocyte quantity and quality under controlled ovarian stimulation? 1.2. Summary Answer Although not statistically significant, a consistent trend was observed favoring the left ovary in fertilization and blastulation rates, suggesting potential lateralized ovarian competence. 1.3. What Is Known Already Anatomical and physiological differences between the ovaries have been described in mammals, including asymmetries in vascularization and ovulatory frequency. However, the functional implications of such asymmetries on human oocyte quality remain unclear. 1.4. Study Design, Size, Duration Prospective multicenter observational study conducted between January 2023 and April 2025 across 11 fertility clinics in Mexico. Data from 12 patients undergoing controlled ovarian stimulation (COS) with complete intraindividual comparison of both ovaries were analyzed. 1.5. Participants/Materials, Setting, Methods Included were women aged 18–39 with regular cycles, AMH between 1.5-5.0 ng/mL, and no comorbidities. COS protocols, ultrasound monitoring, follicular aspiration, and oocyte evaluation were standardized across centres. MII oocyte count, fertilization, and basculation rates were analysed separately for each ovary using paired statistical tests.