Background: Vitamin D3 has been considered as a crucial factor influencing female reproductive health. It plays a vital role in follicular development, oocyte maturation, and subsequent embryo quality, making it an essential factor in assisted reproductive technologies such as fertilization (IVF). Vitamin D3 levels have been positively correlated with ovarian reserve markers and anti-Müllerian hormone (AMH) concentrations, indicating its potential impact on fertility potential. This study aimed to investigate the relationship between oocyte quality and vitamin D3 levels in women undergoing IVF treatment. Materials and Methods: Serum vitamin D3 concentrations were quantified before initiating IVF cycles. A total of 115 oocytes were collected from 35 women, with a mean age of 32 ± 7 years. The quality of the retrieved oocytes was subsequently evaluated by an embryologist. Following the removal of cumulus cells, individual mature oocytes were imaged to evaluate morphometric characteristics. Serum vitamin D levels and oocyte quality were compared between the groups. The patients was used for statistical analysis. Results: The results indicated no significant difference between serum vitamin D levels and the mean ooplasm diameter and area. However, patients with sufficient serum vitamin D levels - cular oocyte shape, standard ooplasm coloration, and a normal polar body shape (less fragmentation of the polar body), and thin and uniform zona pellucida were observed in this group. Conclusion: Low serum vitamin D levels are associated with decreased oocyte quality, and since oocyte quality affects the success rates of IVF, it can be concluded that vitamin D may influence the outcomes of IVF procedures. However, the effects of serum vitamin D levels on reproductive outcomes should be examined in future comprehensive cohort studies. Keywords: Vitamin D, IVF, Quality, Oocytes.

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