Metformin vs. insulin in gestational diabetes. A randomized study characterizing metformin patients needing additional insulin

Diabetes Obes Metab. 2013 Mar;15(3):246-51. doi: 10.1111/dom.12017. Epub 2012 Oct 24.


Aims: We compared metformin with insulin as treatment of gestational diabetes mellitus (GDM). Furthermore, we aimed to characterize metformin-treated patients needing additional insulin to achieve prespecified glucose targets.

Methods: We conducted a single centre randomized controlled study with non-inferiority design comparing metformin and insulin in the treatment of 217 GDM patients having birth weight as primary outcome variable.

Results: There were no significant differences in mean birth weight expressed in grams [+15 (90% confidence interval (CI): -121 to 89)] or SD units [+0.04 (90% CI: -0.27 to 0.18)] between the metformin and insulin groups. There were no significant differences in neonatal or maternal data between the groups. Only 23 (20.9%) of the 110 patients in the metformin group needed additional insulin. Compared with the patients on metformin only, those needing additional insulin were older (p = 0.04), their oral glucose tolerance test had been performed earlier and diabetes therapy started earlier in gestation (p = 0.01 and p = 0.004, respectively). The risk for additional insulin was 4.6-fold in women with baseline serum fructosamine concentration above median compared with those below median.

Conclusions: Metformin is an effective alternative to insulin in the treatment of GDM patients. Serum fructosamine may help in predicting the adequacy of metformin treatment alone.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Birth Weight
  • Blood Glucose / drug effects*
  • Blood Glucose / metabolism
  • Diabetes, Gestational / blood
  • Diabetes, Gestational / drug therapy*
  • Drug Administration Schedule
  • Female
  • Humans
  • Hypoglycemic Agents / blood
  • Hypoglycemic Agents / therapeutic use*
  • Insulin / blood
  • Insulin / therapeutic use*
  • Male
  • Metformin / blood
  • Metformin / therapeutic use*
  • Pregnancy
  • Pregnancy Outcome
  • Treatment Outcome


  • Blood Glucose
  • Hypoglycemic Agents
  • Insulin
  • Metformin