Effect of metformin on in vitro oocyte maturation. The vertical axis represents the percent of oocytes which completed meiosis I (MI) in culture. The horizontal axis shows in vitro metformin concentration (micromolar [μM]). Each experiment utilized 5 mice for each genotype (WT, ob/ob, db/db) with 15 oocytes in each in vitro metformin concentration group per replicate. Each experiment was performed in quadruplicate. Error bars are SEM. Oocytes treated with metformin concentration of 1000 μM demonstrated a reduction in percent oocytes which completed MI compared to control (0 μM) in WT and ob/ob. Asterisks indicate statistical significance of p < 0.05 for WT and ob/ob genotypes following comparison (* and ** p = 0.01, t test).