Endothelial progenitor cells (EPCs) play a role in angiogenesis during pregnancy. The aim of this study was to evaluate circulating EPCs in pregnant women with gestational alterations of glucose tolerance. Glucose tolerance, insulin sensitivity and β-cell function were derived from oral glucose tolerance tests in 23 women with normal glucose tolerance (NGT), 18 with gestational impaired glucose tolerance (GIGT) and 24 with gestational diabetes mellitus (GDM). Circulating cells expressing CD34 in combination with CD133, kinase insert domain receptor (KDR) or both were quantified by flow cytometry. Women with GIGT and GDM had lower CD34(+)KDR(+) and CD34(+)CD133( +)KDR(+) cells at 27±3.2 weeks' gestation compared with NGT (ANOVA p<0.02 for both). CD34(+)KDR(+) and CD34(+)CD133(+)KDR(+) cells were inversely correlated with the area-under-the-glucose-curve (p<0.005, for both) and positively to insulin secretion-sensitivity index (p<0.05, for both). Alterations of glucose tolerance during pregnancy are associated with a decrease in EPCs. Hyperglycaemia might exert a direct effect on depletion of EPCs.