Background: Diabetes, especially the gestational diabetes with its special fetal and maternal disorders, is the most common complication of pregnancy. Both gestational and type II diabetes mellitus are along with a disturbances to insulin secretion as well as insulin resistance. Considering the significant role of zinc in insulin function, the deficiency and importance of this element in gestational diabetes is a matter of consideration.

Materials and Methods: This clinical trial was carried out on 60 pregnants suffering from gestational diabetes, and needing insulin injection from 32^nd week to full-term. The patients were divided into two groups the case group (n=30), received daily zinc sulfate (25mg or 5cc) plus insulin and control group (n=30) received daily placebo (5 cc as syrup) plus insulin until the time of delivery. The required insulin dose was regulated through monitoring fasting blood sugar and blood sugar, 2 h postprandial, every two weeks in both groups. These groups were compared in terms of required insulin dose and maternal/fetal complications. Data were analyzed using t-test, OR, CI, Fisher Exact test, Kolmogorov-Smirnov and Chi-Square tests.

Results: The required dose of insulin had a significant decrease in the case group compared to the control one (p<0.001). However, the mean change in insulin dose in the case and control group compared to the beginning of study was 8.766 (SD:9.63) and 17.533 (SD: 10.54), respectively. The incidence of macrosomia in the case and control groups was significant (P<0.01). The odds ratio of control group compared to the case group was 7. The preeclampsia prevalence in both groups was not significant.

Conclusion: Zinc supplementation in gestational diabetes may lead to the reduction of required insulin dose, incidence of macrosomia and the related complications (e.g., caesarian and delivery dystocia).