Risk of metformin failure in the treatment of women with gestational diabetes

Objectives: To estimate the metformin failure rate in women with gestational diabetes. Methods: The study was designed as a retrospective cohort of women diagnosed with gestational diabetes by the 75 g 2 h oral glucose tolerance test. Women were placed into two groups: metformin success (107 patients not requiring insulin therapy) or metformin failure (15 patients requiring the addition of, or, transition to insulin). Primary outcome: rate of metformin failure. Secondary outcomes: maternal and neonatal factors. Results: The failure rate of metformin was 15% (19/122 women) in the study. The failure group was more likely to have 3 abnormal values on a 2-h 75 g oral glucose tolerance test (37% (n=7/19) vs. 15% (n=15/103), p=0.02). Patients who failed had higher average fasting blood glucose levels on the glucose tolerance test as well as on pretreatment fasting finger stick values. Those who failed metformin were diagnosed with gestational diabetes and started on metformin earlier in gestation. Conclusions: Overall low rate of metformin failure in treatment of gestational diabetes.