Follicular fluid transferrin levels in preovulatory human follicles.

There is transferrin-like protein present in the follicular fluid of stimulated ovarian cycles. The transferrin concentration correlates with the follicular morphologic maturity and steroidogenesis, varies among follicles, and often exceeds serum concentrations. An intermediate range of transferrin concentration is associated with the highest likelihood of oocyte fertilization in vitro. The biological significance of these observations may relate to an optimum degree of follicle maturation.