This study is testing whether daily metformin for 1 year postpartum can reduce risk of diabetes in patients who had gestational diabetes. Typical care for prediabetes after gestational diabetes is counseling on diet and lifestyle. This study is researching whether management of diabetes prevention is more effective with the drug metformin. This study will be conducted at Tufts Medical Center.

Women with a history of gestational diabetes mellitus (GDM) represent a unique population who may benefit from metformin as much as lifestyle intervention; when metformin is prescribed to these women remote from delivery after a diagnosis of prediabetes, it reduces their risk of developing diabetes mellitus (DM) by up to 40% over 10 years. However, in the current system in which gestational diabetes diagnosis, prediabetes testing, and metformin prescription are temporally separated by months to years, less than 20% of postpartum women undergo prediabetes testing. When prediabetes is identified in women with a history of GDM, only 7.8% are prescribed metformin.

Given the increasing public health burden of DM, there is an urgent need to remedy this problem and correct this deficiency in health care delivery that allows so many at-risk women to remain unidentified and untreated.

Compelling preliminary data, confirmed at several other sites, indicates that the postpartum glucose tolerance test to identify individuals with prediabetes can be moved from 4-12 weeks postpartum to 1-4 days postpartum, when women are still hospitalized, with test compliance of 92% and no reduction in sensitivity or specificity for prediabetes.

When individuals with a history of GDM and prediabetes are prescribed metformin, they experience a 50% reduction in DM risk and a 3 kg increase in weight loss over three years compared to placebo. If these same benefits are realized when metformin is initiated soon after delivery, then a simple change in postpartum care so that metformin is routinely prescribed at hospital discharge to women with a history of GDM and prediabetes could improve the health of thousands of women annually by decreasing the number of women who develop DM and fail to achieve postpartum weight loss.

Each year in the United States, approximately 280,000 women are diagnosed with GDM. Without intervention, up to 70% of these women will develop diabetes mellitus (DM) over their lifetime, resulting in devastating health consequences and escalating health care costs. However, implementing a postpartum glucose tolerance test and intervening with metformin for those with prediabetes may be a cost-effective change to postpartum care that would result in a profound decrease in DM incidence.

Inclusion Criteria:

1. Women currently pregnant with planned delivery at Tufts Medical Center
2. Gestational diabetes mellitus diagnosed during pregnancy
3. ≥18 years of age
4. Opted for the 2 hour 75 gram OGTT during postpartum hospitalization
5. Willing and able to sign the informed consent

Exclusion Criteria:

1. Unable to commit to required study visits for any reason.

2. Contraindications to metformin

   • Liver disease
   • Impaired renal function (Creatinine Clearance> )
   • Congestive heart failure(CHF)
   • Taking drugs that could interfere with metformin metabolism

3. Taking metformin outside of pregnancy

4. Prescribed medications for chronic disease that affect glucose metabolism (e.g., long term oral steroids).

5. Decided against the 2 hour 75 gram OGTT during postpartum hospitalization.

6. Preexisting diabetes mellitus.