en <p>Background: Vitamin D supports oocyte development and ovarian steroidogenesis; deficiency is linked to preeclampsia and poor oocyte quality. The purpose of the current study was to investigate the relationship between vitamin D levels and oocyte quality in women undergoing ICSI cycles.<br /> Methods: In this case-control study, 252 women were identified from medical records and classified into high-quality (n=126) and low-quality oocyte groups (n=126). Serum vitamin D levels and anti-M&uuml;llerian hormone (AMH) were recorded. Oocyte quality was assessed by an embryologist using predefined criteria for morphology and maturity. Statistical analysis included Mann&ndash;Whitney tests and multivariable logistic regression (p&lt;0.05). ROC analysis was applied to determine the optimal vitamin D cutoff, reporting AUC, sensitivity, and specificity and statistical significance was set at p&lt;0.05.<br /> Results: Patients in the high-quality oocyte group had a higher median serum vitamin D level compared with those in the low-quality group (25.2 <em>vs.</em> 21.9 <em>ng/ml</em>). Logistic regression showed that sufficient vitamin D levels (&ge;18 ng/ml) were associated with increased odds of having high-quality oocytes (OR=1.85, 95%CI: 1.07&ndash;3.22). AMH levels were also positively associated with oocyte quality (OR=1.42, 95%CI: 1.11&ndash;1.82). The ROC analysis yielded an AUC of 0.61 (95%CI: 0.53&ndash;0.68), indicating modest discriminatory ability.<br /> Conclusion: Serum vitamin D levels are associated with oocyte quality in women undergoing ICSI cycles. While higher vitamin D levels are linked to better oocyte quality, no causal inference can be drawn from this case&ndash;control study design, and interventional studies are needed to evaluate whether correction of vitamin D deficiency improves reproductive outcomes.</p> Anti- mullerian hormone, Assisted reproductive techniques, ICSI, Female infertility, In vitro fertilization, Oocyte quality, Vitamin D 43 50 https://www.jri.ir/article/140296 /documents/fullpaper/en/140296.pdf SaraSadeghitabarFaculty of Medicine, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iran122990AliSadeghitabarMonoclonal Antibody Research Center, Avicenna Research Institute, ACECR, Tehran, Iran61984ZohrehLavasaniDepartment of Obstetrics and Gynecology, Faculty of Medicine, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iranzohrehlavasanii@yahoo.com122992AfsanehMohammadzadehReproductive Biotechnology Research Center, Avicenna Research Institute, ACECR, Tehran, Iranافسانهمحمدزادهaf.mohammadzadeh@yahoo. com684