Background: This study was conducted to determine the effect of gestational diabetes on neuronal density in the dentate gyrus (DG) subfields of hippocampus in rats offspring. Methods: On day 1 of gestation, 10 dams randomly allocated into two control and diabetic groups. Five animals in diabetic group were received 40 mg/kg/BW of Streptozotocin (intraperitoneally) and control animals were received normal saline. Six offsprings of each gestational diabetes mellitus and controls were randomly selected at the day 7, 14 and 21. Infants were scarified and coronal sections were taken from the right dorsal hippocampus and stained with cresyl violet. The number of granular cells and thickness of layers of hippocampus in dentate gyrus lateral (DGl) and dentate gyrus media (DGm) were evaluated. Results: In P7, P14, P21, granular cells numbers of DGm were significantly reduced from (107.6±6.2, 131.6±4.6, 143.5±4.0) in controls to(84.96±2.1, 109.8±7.3, 121.05±5.6)(P<0.05) in cases, respectively and Granular cells of DGl were significantly reduced from (98.76±4.4, 125.6±4.0, 149.9±4.2) in controls to (79.98±4.2, 107.07±8.5, 117.1±6.7)(P;0.05) of cases, respectively. In DGm and DGl, the thickness of the granular and polymorph layers in P7,14 and P21 significantly decreased in gestational diabetics in comparison with controls(p<0.05). Conclusion: This study showed that the uncontrolled gestational diabetes reduces granular neurons of hippocampus in rats offspring
