BACKGROUND: 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). The subpopulation of women with 
BMI≤32 kg/m(2) had no factors showing a significantly different impact on the 
chance of pregnancy for women treated with metformin versus those receiving 
clomiphene treatment or combination metformin/clomiphene treatment versus 
clomiphene treatment. There were no significantly different effects of free 
testosterone, fasting insulin, duration of infertility or ultrasound appearance 
of polycystic ovaries in any treatment groups.
CONCLUSION:   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) . Individual patient data meta-analysis of existing 
randomised trials would clarify this further and would assess whether other 
factors might predict better response to metformin versus standard treatments.