Low vitamin D levels in follicular fluid, but not in serum, are associated with adverse outcomes in assisted reproduction.

Purpose: To assess the relationship between serum/follicular fluid (FF) vitamin D (VD) status and assisted reproductive technology (ART) treatment outcomes among infertile patients.

Methods: A prospective cohort study, including 132 infertile patients scheduled for their first ART treatment cycle, was carried out in a Reproductive Medical Center. Serum and FF samples were collected to assess 25-hydroxy VD [25(OH)D] levels. Low VD level was defined as 25(OH)D concentration of less than 30 ng/mL.

Results: Most infertile patients had low VD levels in serum (88%) and FF (90%). We observed a moderately positive correlation between VD levels in serum and FF (r = 0.34, p < 0.0001). Compared to the group of patients with low VD levels in the FF, those with sufficient VD levels had a significantly higher number of retrieved oocytes (p = 0.03), normal fertilization (p = 0.01), and high-quality embryos (p = 0.001). Moreover, patients with sufficient VD levels in the FF also had significantly higher implantation rates than those with low VD levels (76.92% vs. 46.58%, respectively, p = 0.01) and clinical pregnancy rates (92.31% vs. 61.54%, respectively, p = 0.04).

Conclusion: These data collectively revealed that low VD levels in serum and FF were common among infertile patients. VD levels in FF, but not in serum, were associated with embryo quality, normal fertilization, implantation rates, and clinical pregnancy rates. Further studies are mandatory to determine the molecular mechanism and VD's potential therapeutic benefits in infertile patients.