STUDY DESIGN: Mean maternal corticotropin-releasing hormone levels were studied in women who met specific criteria for preterm labor and in women with normal pregnancies. Levels were also compared in the latent and active phases during term labor.

RESULTS: In pregnancies complicated by preterm labor, maternal corticotropin-releasing hormone levels were higher than in normal pregnancies; this elevation occurred before labor was diagnosed clinically (p < 0.05). When preterm labor was associated with infection, the mean levels were not elevated. Mean plasma levels were similar in latent and active phases during labor at term.

CONCLUSION: Maternal plasma corticotropin-releasing hormone levels are elevated in association with preterm labor. This elevation does not appear to be due to labor itself and may reflect an early activation of the placenta before the onset of preterm labor.