Aim The aim of this study was to analyze whether urocortin-1 concentration in midtrimester amniotic fluid could serve as an indicative marker of preterm labor. Material and Methods A retrospective cohort study was conducted. Urocortin-1 concentrations in midtrimester amniotic fluid were measured in 22 pregnant women with preterm deliveries and 45 women who delivered at term using enzyme-linked immunosorbent assay. Results The median amniotic fluid urocortin-1 concentration was significantly lower in the women with preterm birth (40.06pg/mL; range, 13.77-67.58pg/mL) than in the women who gave birth at term (49.56pg/mL; range, 26.25-175.9pg/mL; P=0.022). The result of receiver-operator curve analysis indicates that an amniotic fluid urocortin-1 concentration57.88pg/mL had an area under the curve of 0.673 (95% confidence interval, 0.55-0.78; P=0.01) with a sensitivity of 81.8%, specificity of 40.0%, positive predictive value of 40%, and a negative predictive value of 82% in identifying which of the patients subsequently delivered prematurely. Conclusions These results suggest that low urocortin-1 concentration in midtrimester amniotic fluid could be used as an indicative marker of preterm birth.