The frequency of preterm labour has risen over the last few years. Plasma oestrogen concentrations differ between patients who deliver before term and those who deliver at term. Oestrogen can influence the kinetics of circulating endothelial progenitor cells (cEPCs). Here, we attempted to identify the potential association of cEPCs with the incidence of complications typical of prematurity. The study groups consisted of 60 pregnant women with premature rupture of membranes (PROM; less than 37 weeks) and 50 term pregnant women (more than 38 weeks). cEPCs were isolated from term pregnant women and pregnant women with PROM and then migratory, proliferative, tubulogenic and functional properties of these cells along with serum secretion of important EPC chemotactic cytokines were analysed. In addition, the effect of 17β-oestradiol on biological features of cEPCs harvested from pregnant women was investigated. Our results showed that an increased concentration of oestrogen in women with PROM was associated with increased numbers of cEPCs, with these cells having increased oestrogen receptor α expression together with augmented proliferative, migratory and colony-formation properties. 17β-oestradiol induced proliferation, migration and angiogenic secretory activity of cEPCs from pregnant women. Overall, circulation mobilisation of EPCs in pregnant women may be associated with placental disorders.