FIELD : medicine.SUBSTANCE : invention relates to the field of medicine, in particular to obstetrics, and is intended to predict preterm labor. Using indicators of the concentration of the total amount of extracellular DNA (ovDNA) and the concentration of IL-8 in peripheral blood plasma in pregnant women at 22-36 weeks of gestation, the variable P is determined. At P?>?0.5, preterm labor will occur. When P?≤?0.5, preterm labor will not occur.EFFECT : invention provides an effective prediction of preterm labor by the joint determination of ovDNA and neutrophil-activating factor in peripheral blood plasma.1 cl, 1 dwg, 3 ex