Objectives: To evaluate whether polycystic ovarian syndrome (PCOS)-associated infertility is related to alterations of leptin, leptin receptor (Ob-R) and p-STAT3/SOCS3 system in the ovary.

Design and setting: A case-control study conducted in a university hospital.

Patients: Thirty-one infertile PCOS women with oligo-ovulation plus polycystic ovarian morphology and seventy-nine infertile women with tubal blockage (control). The subjects were stratified according to IVF outcomes: successful and failed subgroups.

Methods: Serum and follicular fluid (FF) leptin levels were measured with ELISA. RT-PCR and Western blotting were performed to assess expression of mRNA encoding leptin and Ob-R and proteins of p-STAT3 and SOCS3 in granulosa cells (GCs).

Results: Leptin levels in serum and FF of PCOS women were significantly higher than those of control (P<0.01). There were no significant differences in expression of leptin mRNA, short and long Ob-Rs between PCOS and control (P>0.05). P-STAT3 level was decreased in PCOS compared with control (P<0.01), whereas SOCS3 remained significantly unchanged (P>0.05). Further analysis showed that serum and FF leptin levels were significantly higher, while p-STAT3 in GCs was lower in failed subgroup of PCOS than those in successful subgroup of PCOS (P<0.05).

Conclusion: Hyperleptinemia and high FF leptin are important pathologies of PCOS with infertility. Lower levels of p-STAT3 in GCs may be related to ovarian leptin resistance and fecundity in PCOS women. Relatively high serum and FF leptin and low p-STAT3 in GCs may account for decreased fertilization, implantation and pregnancy rates of IVF in PCOS women.