The investigators intend to conduct a prospective, randomized, double-blind placebo controlled range-finding study to measure the effects of early metabolic intervention with metformin in women at risk for GDM before the commencement of pregnancy or prior to completion of the first trimester. The target sample size for this pilot study is 100 women. The effect size observed will provide preliminary data for a subsequent study which will be sufficiently powered to detect small or moderate effects from early metabolic intervention in women at risk for GDM.