Placenta is the most accurate record of the infant prenatal experience. If the placenta is examined minutely after delivery, it provides much insight into the prenatal health of the baby and the mother. The weight of placenta is higher in diabetic pregnancy in comparison to the normal pregnancy. To study the cellular changes that might contribute to more weight of placenta in diabetic pregnancies, light microscopic and electron microscopic analysis was performed. Twenty singleton pregnancies complicated with Gestational diabetes mellitus (12 controlled on diet, 8 controlled on insulin) were selected and compared to control group. Tissue sections were processed and analyzed. The placenta of diabetic pregnancies showed no abnormality on gross observation but light microscopic examination revealed, lesions like syncytial knots, fibrinoid necrosis, villous edema, villous fibrosis and capillary proliferation. Transmission electron microscopic examination (TEM) showed changes in almost all the layers of the placental membrane i.e. synctiotrophoblast, cytotrophoblast, trophoblastic basement membrane and fetal capillaries. These changes were observed in the placenta of both groups of patients whether blood sugar level was controlled by diet or insulin, but to different degree. It indicates that control of hyperglycemia only partially prevents the development of placental abnormalities which must be due to some other constituent factor of diabetic state.