WASHINGTON – Metformin’s role in preventing or delaying the onset of type 2 diabetes in women with a history of gestational diabetes mellitus has been firmly established by the Diabetes Prevention Program (DPP) trial – most recently, by 15-year follow-up data reported this year – and the drug should be front and center for clinicians who hope to stave off the “remarkable” incidence of type 2 diabetes after GDM, Robert E. Ratner, MD, maintained at the biennial meeting of the Diabetes in Pregnancy Study Group of North America.
Dr. Robert E. Ratner
The DPP included “the single largest population of women with a history of GDM that’s been looked at in a randomized controlled trial,” and considering its multiethnic population, the trial offers a reliable representative sample to ponder today when evaluating long-term use of metformin after GDM, said Dr. Ratner, a principal investigator of the National Institutes of Health–sponsored DPP and the DPP Outcomes Study and a former chief scientific & medical officer for the American Diabetes Association.
The drug stacked up equally to lifestyle interventions among DPP participants who had a history of GDM, but it’s important to appreciate that these interventions were intensive and that metformin is inexpensive, well tolerated, and “has a long safety record,” he said.
Results of follow-up out to 15 years
Of the more than 3,000 men and women enrolled in the landmark DPP, conducted during 1996-2001, 350 were women with a documented history of GDM and over 1,400 were women who had deliveries but no history of GDM. All participants had impaired glucose tolerance – defined for the trial as having both a fasting plasma glucose value of 95-125 mg/dL and a 2-hour value of 140-199 mg/dL after a 75-g glucose load – and were randomized to placebo, metformin, or intensive lifestyle intervention.
Metformin therapy reduced the incidence of diabetes by approximately 50% in women with a history of GDM, compared with the placebo group – as did lifestyle – over 3 years. The number needed to treat to prevent one case of diabetes was five. Women without a history of GDM, on the other hand, saw only a 14% reduction with metformin when compared with placebo (and a 49% reduction with lifestyle).
“In women with a history of GDM ... one pill twice a day for $4 a month worked as well as intensive lifestyle [change],” Dr. Ratner said, referring to the initial GDM-specific analysis of DPP data published in 2008 (J Clin Endocrinol Metab. 2008;93[12]:4774-9).
In a 10-year postrandomization follow-up, published in 2015, both metformin and lifestyle continued to be equally effective for the GDM group, reducing the progression to diabetes by 40% and 35%, respectively (J Clin Endocrinol Metab. 2015;100:1646-53). The number needed to treat to prevent one case of diabetes was seven. (Among women without a history of GDM, metformin did not reduce progression to diabetes.)
A recent DPP Outcomes Study analysis of metformin’s impact on diabetes prevention at 15 years, moreover, showed a 41% risk reduction among women with a history of GDM (Diabetes Care. 2019;42[4]:601-8).