Metformin Is an Effective Alternative to Insulin in Gestational Diabetes Mellitus

In patients with gestational diabetes mellitus, metformin is an effective alternative to insulin, according to the findings of a recent single-center randomized controlled study.¹
   
Gestational diabetes mellitus affects an estimated 2% to 10% of all pregnancies.² Although many women with a diagnosis of gestational diabetes can manage the condition with dietary restrictions, insulin may be needed when dietary changes alone do not achieve near-normal blood glucose levels. The oral antihyperglycemic drug metformin-a pregnancy Category B medication-has been shown to effectively control insulin levels and has greater ease of use than insulin, which must be injected. However, many obstetricians are reluctant to prescribe metformin during pregnancy because it crosses the placental barrier, creating potential for teratogenic effects.
   
To compare the effectiveness of metformin and insulin for achieving blood glucose level targets and to evaluate the need for rescue insulin in metformin patients, researchers randomized 217 patients with gestational diabetes mellitus to either insulin alone (n=107) or metformin with insulin as needed (n=110). The primary outcome variable was infant birth weight.
   
No significant differences in mean birth weight and in neonatal or maternal data were found between treatment groups. Of the 110 patients in the the metformin group, 23 (20.9%) required additional insulin to achieve prespecified blood glucose level targets. The women in the metformin group who needed insulin, compared with those in the metformin group who did not require insulin, tended to be older (P=0.04), to have had an oral glucose tolerance test conducted earlier in their pregnancy (P=0.01), and to have initiated treatment for gestational diabetes earlier in their pregnancy (P=0.004).
   
Of interest was that women who had a baseline serum fructosamine concentration above the median value (unspecified in the study abstract) were 4.6 times more likely to need additional insulin than those who had a baseline concentration below the median value. This finding, according to the study authors, suggests that serum fructosamine concentrations may help play a role in predicting the adequacy of metformin treatment alone.
   
Although larger studies are needed to determine the safety of metformin during pregnancy, these findings, along with the findings of other smaller studies, show that metformin is an effective alternative to insulin for the management of blood glucose levels. An additional benefit of metformin, which is administered orally, may be an improvement in medication adherence rates.

Pertinent Points:
- Metformin is an effective alternative to insulin in patients with gestational diabetes.
- The birth weight of infants did not differ significantly between the metformin and insulin groups.

References:

1. Tertti K, Ekblad U, Koskinen P, et al. Metformin vs insulin in gestational diabetes: a randomized study characterizing metformin patients needing additional insulin. Diabetes Obes Metab. 2013;15(3):246-251.
2. National Diabetes Information Clearinghouse. National Diabetes Statistics, 2011. Available at: http://diabetes.niddk.nih.gov/dm/pubs/statistics/. Accessed March 12, 2013.