Free 25(OH)D3 levels in follicular ovarian fluid top-quality embryos are higher than non-top-quality embryos in the normoresponders group

Vitamin D and calcium in follicular fluid play an important role in modulating steroidogenesis, folliculogenesis, and oocyte quality determination. Both collaborate to produce top-quality embryos (TQE) during in vitro fertilization (IVF). In this study, we compared free 25(OH)D3 and calcium levels in follicular fluid between TQE and non-TQE groups. This cross-sectional study included women who underwent IVF procedures at tertiary hospitals in Bandung, Indonesia. Ovarian follicular fluid was collected during the ovum pick-up procedure. The examination of 25(OH)D3 levels, vitamin D-binding protein, and calcium in the follicles was done using an enzyme-linked immunosorbent assay (ELISA). Free 25(OH)D3 levels were calculated using the Vermeulen formula. A total of 173 samples met the study criteria, including 86 subjects in the TQE group and 87 subjects in the non-TQE group. There was a significant difference in free 25(OH)D3 follicular fluid levels between the TQE and non-TQE groups (p = 0.017); however, there was no significant difference in calcium levels between the two groups (p = 0.805). We also found that there was a significant association between free 25(OH)D3 follicular fluid levels and embryo quality (OR 3.05, 95% CI 1.46-6.38; p-value = 0.002); however, there was no significant association between follicular fluid calcium and embryo quality [p = 0.144 and OR, 1.74 (95% CI 0.82-3.68)]. The results suggest that free 25(OH)D3 and calcium in the follicular fluid act independently during steroidogenesis, folliculogenesis, and fertilization.