FST and polycystic ovary syndrome: Multiple studies have reported that serum FST concentrations are significantly elevated in women with PCOS compared with healthy controls,[34,35] whereas 1 study found no significant difference in FST levels within follicular fluid between PCOS and non-PCOS individuals.[36] This suggests that serum FST may better reflect systemic or metabolic aspects of the disease, while follicular fluid FST levels could be more closely tied to local ovarian microenvironments.