Comparison of Insulin Alone to Insulin With Metformin to Treat Gestational Diabetes Mellitus

Inclusion Criteria:

• Able to read and write English and/or Spanish and give written consent
• Diagnosis of GDM, defined as an abnormal glucose tolerance test performed after 12 weeks gestation using 1 of the 2 criteria below:
• 50 gram 1 hour oral diabetes screening testing yielding a result of > 200 mg/dL
• A 100 gram 3 hour oral glucose tolerance testing yielding >2 abnormal values (normal values defined as fasting blood glucose < 95, 1 hour < 180, 2 hour < 155 and 3 hour < 140)
• Singleton gestation
• Gestational age between 12 and 34 weeks and 6 days determined by last menstrual period (LMP) confirmed by ultrasound using criteria set forth by the ACOG (Committee on Obstetric Practice). If LMP is unknown then gestational age must be set by ultrasound prior to 20 weeks gestation.

Exclusion Criteria:

• Pre-existing DM either by diagnosis preceding pregnancy or hemoglobin A1c >6.5 collected during the current pregnancy
• Uncontrolled chronic hypertension, as this may alter maternal and perinatal outcomes measured.
• Multiple gestations
• Major fetal anomalies anticipated to require NICU admission
• Contraindication to metformin (allergy, history of lactic acidosis, pre-existing renal disease (Cr >1.5 mg/dL), active liver disease, current alcohol abuse).
• Vitamin B12 deficiency, as metformin reduces intestinal absorption of vitamin B12
• Medications known to effect glucose metabolism other than insulin and metformin as this may mask any effect between the two treatments.
• Known inability to tolerate metformin.