The purpose of this study was to examine the utility of a single second-trimester plasma corticotropin- relasing hormone measurement as a marker for preterm delivery in women at high risk for preterm delivery. Study design: This is an analysis of data from a multicenter placebo-controlled trial designed to evaluate the role of 17 alpha hydroxyprogesterone caproate (17P) in the prevention of recurrent preterm birth. Women with a documented history of a previous spontaneous preterm birth at < 37 weeks were enrolled (16- 20 wks) and randomly assigned in a 2 to 1 ratio to weekly injections of 17P or matching placebo. Blood was collected before treatment in 170 patients (113 assigned 17P and 57 placebo) who were enrolled at 11 of the 19 centers. Plasma levels of corticotropin-releasing hormone were compared between those who delivered preterm and those delivering at term. Data were analyzed using the Wilcoxon rank-sum test. Results: The overall rates of preterm birth in this cohort of 170 patients were 35.9% at < 37 weeks (31.9% progesterone, 43.9% placebo), and 19.4% at < 35 weeks (18.6% vs 21.1% ). The median levels of corticotropin-releasing hormone were similar between those delivering at < 37 weeks and those delivering ≥ 37 weeks (0.39 ng/mL vs 0.37 ng/mL, P = .08). In addition, there were no differences in corticotropinreleasing hormone levels among those who delivered at < 35 weeks or ≥ 35 weeks (0.36 vs 0.38, P = .90). Moreover, there were no differences in corticotropin-releasing hormone levels among those in the placebo group who delivered at < 37 or ≥ 37 weeks (0.40 vs 0.41, P=.72) and at < 35 or ≥ 35 weeks (P=.64). Conclusion: A single measurement of corticotropin- releasing hormone at 16 to 20 weeks’ gestation is not a good biomarker for recurrent preterm delivery in patients at high risk for this complication. The purpose of this study was to examine the utility of a single second-trimester plasma corticotropin- relasing hormone measurement as a marker for preterm delivery in women at high risk for preterm delivery. Study design: This is an analysis of data from a multicenter placebo -controlled trial designed to evaluate the role of 17 alpha hydroxyprogesterone caproate (17P) in the prevention of recurrent preterm birth. Women with a documented history of a previous spontaneous preterm birth at <37 weeks were enrolled (16-20 wks) and randomly assigned in a 2 to 1 ratio to weekly injections of 17P or matching placebo. Blood was collected before treatment in 170 patients (113 assigned 17P and 57 placebo) who were enrolled at 11 of the 19 centers. Plasma levels of corticotropin-releasing hormone were compared Between those who delivered preterm and those delivering at term. Data were analyzed using the Wilcoxon rank-sum test. Results: The overall rates of preterm birth in this cohort of 170 p The median levels of corticotropin-releasing hormone were similar between those delivering at <37 weeks (31.9% progesterone, 43.9% placebo), and 19.4% at <35 weeks (18.6% vs 21.1%). and those delivering ≥ 37 weeks (0.39 ng / mL vs 0.37 ng / mL, P = .08). In addition, there were no differences in corticotropin secretion hormone levels among those who delivered at <35 weeks or ≥ 35 weeks (0.36 vs 0.38 , P = .90). Moreover, there were no differences in corticotropin-releasing hormone levels among those in the placebo group who delivered at <37 or ≥ 37 weeks (0.40 vs 0.41, P = .72) and at <35 or ≥ 35 weeks (P = .64). Conclusion: A single measurement of corticotropin-releasing hormone at 16 to 20 weeks’ gestation is not a good biomarker for recurrent preterm delivery in patients at high risk for this complication.