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

The objective of this study is to compare the effectiveness of insulin alone vs the
combination of insulin and metformin in treating patients with gestational diabetes (GDM).
Currently, outside of pregnancy, the treatment of type 2 diabetes mellitus (T2DM) with both
metformin and insulin is superior to using insulin alone. In pregnancy, insulin alone has
traditionally been used, though some advocate the use of metformin alone as primary therapy.
There have been no trials published to date specifically comparing combination therapy to
insulin alone. Our hypothesis is that the combination of metformin and insulin will improve
overall control of blood glucose, the improvement of which has been demonstrated to improve
maternal and neonatal outcomes. Control of blood glucose will be determined by hemoglobin A1c
at the time of delivery.

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.