SHBG and polycystic ovary syndrome: VAI: visceral adiposity index, PCOS: polycystic ovarian syndrome, SHBG: sex hormone binding globulin, DHEAS: dehydro-epiandrosterone, OGTT: oral glucose tolerance test, HDL: high-density lipoprotein, TG: triglyceride, AFC: antral follicle count, HOMA-IR: homeostatic model assessment of insulin resistance, FAI: free androgen index