Question: What are the clinical trial outcomes of metformin use in polycystic ovary disease?

Context:
It has been demonstrated that by reducing hyperinsulinemia, in particular with the administration of metformin, insulin-lowering agents might improve endocrine and reproductive abnormalities in PCOS patients.
Metformin has failed to gain wide acceptance as a first-line treatment option for women with anovulatory infertility related to polycystic ovary syndrome. This study aimed to ascertain factors that predict fertility success with treatment that included metformin compared to standard (non-metformin) treatment. METHODS: Randomised trial data analysis by logistic regression of factors likely to have a differential influence on the likelihood of success of metformin versus non-metformin treatment amongst women with ovulation dysfunction related to polycystic ovary syndrome. RESULTS: metformin versus those receiving placebo and those with lower BMI who received metformin were more likely to become pregnant than their lower BMI counterparts who received placebo (P=0.039).
This study provides preliminary evidence that BMI may be an important prognostic factor in response to metformin for women with ovulation dysfunction related to polycystic ovary syndrome, suggesting that women with a lower BMI may respond better to metformin treatment versus placebo amongst women with BMI>32 kg/m(2)
A prospective comparative study including 63 patients with PCOS has been done during 2 years. Women were randomly allocated to clomifene + Metformin (Metformin group, Metformin took during 8 weeks, 850 mg twice a day, plus Clomifene 100 mg per day during five days) or Clomifene only (100 mg per day during five days)
Our conclusion is that Metformin is an effective addition to Clomifene Citrate in term of reestablishment of ovulation and full-term pregnancies achievement, excluding ART cycles.
A prospective, randomized, double-blind 26 week long study was undertaken in 50 women with PCOS. They all received diet and lifestyle counselling, and metformin 850 mg three times daily.
nti-Müllerian hormone (AMH) levels reflect the number of small antral follicles in the ovaries and are elevated in PCOS.
Six months of androgen suppression by either metformin or low-dose dexamethasone treatment failed to influence circulating AMH levels.
The effect of metformin on serum AMH concentrations, follicle number and ovarian volume was studied in 26 women (aged 20-41 years) with PCOS after 6 months of treatment
Serum AMH levels, the number of antral follicles and ovarian volume decreased significantly during metfromin treatment.
Metformin treatment before IVF/ICSI in women with polycystic ovary syndrome; a prospective, randomized, double blind study.
investigate the effect of pre-treatment with metformin in women with polycystic ovary syndrome (PCOS) scheduled for IVF stimulation.
Pre-treatment with metformin prior to conventional IVF/ICSI in women with PCOS does not improve stimulation or clinical outcome. However, among normal weight PCOS women, pre-treatment with metformin tends to improve pregnancy rates.
Treatment of 10 insulin-resistant PCOS women with metformin significantly increased circulating fasting ghrelin concentrations
double-blind, placebo-controlled approach with detailed assessment of ovarian activity
The effect of metformin on follicular maturation was rapid, because the E2 circulating concentration increased over the first week of treatment only in the metformin group. Significant (P < 0.01) weight loss (and leptin reduction) was recorded in the metformin group, whereas the placebo group actually increased weight (P < 0.05). A significant increase in circulating high-density lipoprotein was observed only in the metformin-treated group. Metabolic risk factor benefits of metformin treatment were not observed in the morbidly obese subgroup of patients (body mass index > 37). No change in fasting glucose concentrations, fasting insulin, or insulin responses to glucose challenge was recorded after 14-wk metformin or placebo therapy.
We show in a large randomized placebo-controlled trial that metformin treatment improves ovulation frequency in women with abnormal ovarian function and polycystic ovaries significantly but to a modest degree, and protracted treatment improves cardiovascular risk factors. These data support a beneficial effect of metformin in improving ovarian function in women with oligomenorrhea and polycystic ovaries.
studies evaluating metformin treatment in women with clomiphene citrate (CC)-resistant polycystic ovaries (PCO)
There was no improvement in the ovulation rate despite a significant reduction of body mass index, serum testosterone and fasting leptin concentrations in the metformin group.

Answer: 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.