AMH and polycystic ovary syndrome: Additionally, serum AMH levels significantly slid down in PCOS patients with no more than 6 months metformin treatment (SMD − 1.38, 95%CI − 2.18 to − 0.58, P = 0.0007) (Fig. 4), or with no more than a dose of 2000 mg/day (SMD -0.70, 95% CI -1.11 to -0.28, P = 0.001) (Fig. 5).