Levels of maternal plasma corticotropin-releasing factor and urocortin during labor

Corticotropin-releasing factor (CRF) is produced by the placenta and intrauterine tissues and secreted in increasing amounts from early to term pregnancy. In the presence of labor, a more incisive increase in CRF levels has been described, and women with preterm labor or those destined to have premature delivery have higher midpregnancy CRF levels than those who deliver at term. Urocortin is a 40-amino acid peptide belonging to the CRF family, expressed by human trophoblast and fetal membranes, which has the same biologic effects as CRF. Acting on the same CRF receptors, urocortin stimulates myometrial contractility and ACTH and prostaglandin release from cultured human placental cells. Because no data exist about urocortin levels in the maternal circulation at parturition, we investigated whether maternal plasma urocortin and CRF levels change according to cervical dilatation in healthy pregnant women at term labor.

In a cross-sectional study of labor, a single maternal blood sample was collected from healthy pregnant women at term (n = 40); in a second longitudinal study, plasma samples were collected longitudinally in a subset of patients (n = 8) throughout labor, according to a Bishop score evaluation.

Both maternal plasma CRF and urocortin levels were higher in labor than those previously reported during pregnancy, but they did not change significantly during the different stages of labor when evaluated longitudinally. Some patients showed a trend toward increasing levels, whereas others had variable concentrations.

Neither CRF nor urocortin levels changed during the progression of spontaneous labor.