PCOSMIC Trial - PolyCystic Ovary Syndrome, Metformin for Infertility With Clomiphene

Inclusion Criteria: * Women between the age of 18 and 39 years inclusive. * Anovulatory infertility of duration at least 12 months. * Polycystic ovary syndrome, based on Rotterdam consensus criteria. * Normal serum prolactin, thyroid function and 17-hydroxyprogesterone. * Normal serum prolactin, thyroid function and 17-hydroxyprogesterone; Exclusion Criteria: * Presence of any other significant infertility factor including male factor, known tubal disease or history of an ectopic pregnancy, known endometriosis affecting the fallopian tubes or ovaries. * Already taking oral hypoglycaemics. * Diabetics receiving treatment. * Renal impairment * Chronic hepatic disease * Cardiac Disease * Alcohol dependency * Pre-disposition to lactic acidosis * Previous ovarian drilling procedure, gonadotrophin injection therapy, IUI (intrauterine insemination) or IVF ( in vitro fertilisation). * For those women who have had previous fertility treatment, the following would be excluded: * Women who have had \> 5 cycles of clomiphene citrate * Women who have had \> 5 months metformin treatment previously * Women who have proven to be resistant to 100mg or more of clomiphene citrate.