Association of Serum Phoenixin-14 and Phoenixin-20 with Diminished Ovarian Reserve

Background/Objective: Phoenixin (PNX), a recently identified neuropeptide, has been shown to regulate the hypothalamic-pituitary-gonadal axis and play a role in folliculogenesis and oocyte maturation. However, its clinical relevance in ovarian reserve remains unclear. This study aimed to evaluate the association between serum PNX-14 and PNX-20 levels and ovarian reserve and to determine whether these peptides provide additional information regarding ovarian reserve status in women with diminished ovarian reserve (DOR). Methods: This prospective case-control study included 160 women of reproductive age. Participants were categorized according to anti-Müllerian hormone (AMH) levels and antral follicle count (AFC). Serum PNX-14 and PNX-20 levels were measured using ELISA. Statistical analyses included group comparisons, Spearman correlation, receiver operating characteristic (ROC) analysis, and logistic regression. Results: PNX-14 levels differed significantly across AMH-defined groups (p < 0.001), with higher levels observed in women with DOR. In contrast, PNX-20 levels showed no significant differences (p = 0.305). PNX-14 demonstrated excellent diagnostic performance for identifying DOR (AUC = 0.921), with a sensitivity of 78.7% and a specificity of 95.3% at a cut-off value of 183 pg/mL. A significant negative correlation was found between AMH and PNX-14 (r = -0.639, p < 0.001), whereas PNX-20 showed no significant correlation. In logistic regression analysis, PNX-14 was significantly associated with DOR in unadjusted and partially adjusted models; however, this association was attenuated after adjustment for AFC. Conclusions: PNX-14 is significantly associated with ovarian reserve status and may provide complementary information regarding DOR when interpreted alongside established ovarian reserve markers. In contrast, PNX-20 does not appear to have clinical utility in this context.