What are the clinical trial outcomes of metformin use in polycystic ovary disease?
Metformin treatment vs placebo significantly but modestly improves ovulation frequency in women with abnormal ovarian function/oligomenorrhea and polycystic ovaries,  the lower BMI women were more likely to become pregnant.  While in naturally conceiving normal weight PCOS women pre-treatment with metformin tends to improve pregnancy rates, pre-treatment with metformin prior to conventional IVF/ICSI in women with PCOS does not improve stimulation or clinical outcome.
Metformin is an effective addition to Clomifene Citrate in term of reestablishment of ovulation and full-term pregnancies achievement.
Studies on the effect of metformin on serum Anti-Mullerian Hormone levels /AMH concentrations bring conflicting results, from Metformin having no effect on AMH  to Metformin treatment resulting in significant decrease of AMH levels, antral follicle numbers and ovarian volume. 
Metformin has been shown to cause significant weight loss (and leptin reduction) in PCOS.