Objective: Calcitonin gene-related peptide (CGRP) circulates in maternal circulation throughout pregnancy, and specific receptors for CGRP (CGRPrs) are expressed by human myometrium. Because CGRP induces a dose-dependent relaxation of human myometrium, we examined a role for CGRP in modulation of myometrial smooth muscle contractility during pregnancy and labor. The aim of the present study was to evaluate the changes of maternal serum CGRP levels during parturition, according to the mode of delivery and in relation to cervical dilatation.
Methods: Circulating CGRP levels were measured in the following groups of healthy women: nonpregnant women, during the follicular phase of the menstrual cycle (n = 19); at term pregnancy (39-40 weeks; n = 24); after elective cesarean delivery (39-40 weeks; n = 20); and at spontaneous vaginal delivery (39-40 weeks; n = 16). In a subgroup of women, blood samples were collected longitudinally throughout labor at various cervical dilatations in the progress of labor (n = 8).
Results: Pregnant women at term not in labor had significantly higher CGRP levels than nonpregnant women (P =.021). No significant difference was found between women who delivered vaginally and those who had elective cesarean, and there were no correlations between CGRP plasma levels and cervical dilatation.
Conclusions: Parturition is characterized by no significant changes in maternal serum CGRP levels, and no significant correlation exists between plasma CGRP levels and cervical dilatation during labor.