In the present invention, thanks to a prospective multicenter cohort study including 200 pregnant patients with five-serum sampling per patient, inventors investigated the concentrations of protein biomarkers in the plasma of high risk pregnant women during the second and third trimesters to predict spontaneous preterm birth. Inventors demonstrated that PROK1 (Prokineticin 1) also called EG-VEGF (Endocrine Gland-derived Vascular Endothelial Growth Factor), is secreted by the placenta and exhibits increased serum levels in patients with sPTB, before 37 weeks of gestation, compared with uncomplicated pregnant women. More precisely, Women with spontaneous preterm birth exhibited higher concentrations of serum PROK1/EG-VEGF than uncomplicated patients at 20 weeks, 24 weeks, 28 weeks and 32 weeks. Accordingly, serum PROK1/EG-VEGF concentrations could be considered as biomarker of spontaneous preterm birth in high-risk pregnant women