Phosphate concentrations in follicular fluid during assisted reproductive treatment: relevance for ovarian function and fertility outcomes.

Background: The role of follicular fluid phosphate for reproductive health and oocyte maturation is unclear. This study investigates the relationship between follicular fluid vs serum phosphate concentrations and the possible link with sex steroids during in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) at a Danish fertility clinic.

Methods: A prospective cohort of infertile women who attended Danfert Fertility clinic (Copenhagen, Denmark) and received IVF or ICSI treatment between June 2015 and February 2017. Correlation analyses were performed with Spearman's Rank or Pearson's correlation, while categorical variables were analyzed with Chi-squared test.

Results: In total, 110 participants were included in the study, and 33 of these achieved a live birth. Phosphate concentrations were higher in the follicular fluid compared to corresponding serum samples (1.16 mmol/L vs. 1.06 mmol/L, p = 0.002) and there was a positive correlation between serum and follicular fluid phosphate concentrations (r = 0.43, p = 0.007). A positive trend was also found for calcium concentrations, though not statistically significant (r = 0.31, p = 0.060). Correlation analysis also showed a positive correlation between concentrations of phosphate and calcium in follicular fluid (r = 0.41, p < 0.001). A positive correlation was observed between concentrations of phosphate and testosterone in follicular fluid (r = 0.34, p < 0.001). When stratified into tertiles, we found no significant differences between live birth rates in follicular fluid phosphate (p = 0.624), calcium (p = 0.207), or testosterone (p = 0.841).

Conclusions: This study found that follicular fluid phosphate concentrations are higher than serum phosphate concentrations, suggesting possible local regulation. However, no significant association was found between follicular phosphate and ART outcomes. Further research is needed to explore its potential role in reproductive physiology.

Clinical trial: Clinicaltrials.gov (NCT02437578; registration date 2015/04/16).