Placental damage may be responsible for the fetal complications in pregnancies complicated by diabetes. We have analyzed the prevalence of gestational diabetes (GD) in a population of 109 pregnant women, the risk factors and the placental changes associated with gestational diabetes. Tests carried out were oral glucose tolerance test at 24-28 weeks of gestation, using the IADPSG (International Association of Diabetes and Pregnancy Study Groups) criteria for gestational diabetes, glycated hemoglobin, fasting insulin, total cholesterol, high density lipoprotein (HDL)-cholesterol, low density lipoprotein (LDL)-cholesterol, triglycerides, two-dimensional (2D) ultrasound and, also, there were analyzed macro and microscopic placental fragments from pregnant women with÷without GD. It has been recorded the weight of placenta at birth and there were analyzed the possible pathological changes. The prevalence of GD was 11.9%. We have applied the direct logistic regression to determine the impact of some factors over the probability of association with gestational diabetes. The most powerful predictor was the placental maturity grade, the patients with decreased maturity grade having chances 52.6 times higher than those with an increased placental maturity grade to associate gestational diabetes. Sizes of placentas in patients with gestational diabetes mellitus were significantly increased than in patients without this diagnosis (p=0.012) from week 24-28. Pathological changes were discovered in six of the 13 placentas of women with gestational diabetes mellitus, independent of the level of glycated hemoglobin (p=0.72). The level of hyperglycemia is only partially associated with the presence of placental changes, which may be caused by other maternal factors.