Metformin Vs. Insulin in Gestational Diabetes. A Randomized Study Characterizing Metformin Patients Needing Additional Insulin

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.