RESUMO
BACKGROUND: Proinflammatory cytokines are increased in maternal blood at term pregnancy and are associated with cervical ripening and the initiation of labor. We hypothesize that maternal plasma cytokines also affect the sensitivity to labor pain. METHODS: By using a previously validated model describing labor pain, we used a deidentified database derived from healthy nulliparous parturients who delivered singleton pregnancies at term. Numerical rating scores for pain were recorded after the onset of regular contractions using an 11-point scale. Maternal blood was drawn for the measurement of interleukin (IL)-1ß, IL-4, IL-6, IL-8, and IL-10; interferon-γ; and tumor necrosis factor-α on admission or at the onset of painful contractions, whichever occurred later. Individual demographic, physiognomic, and cytokine variables that significantly affected labor pain at P < 0.05 were reported and included stepwise into a multivariable model. RESULTS: One hundred sixty parturients provided 411 numerical analog scores for pain that were evaluated with our model. The relationship between numerical analog scores and cervical dilation was significantly affected by the type of membrane rupture, membrane status, induction, oxytocin administration, maternal race, and plasma IL-1ß concentration as individual variables. Only the association between the highest IL-1ß quartile and slower acceleration of pain during labor remained significant in the multivariate model (P = 0.0003). Women with IL-1ß concentration in the highest quartile arrived at the labor room with a more dilated cervix than those with lower plasma concentrations of IL-1ß (5.1 ± 3.0 vs 4.1 ± 2.6 cm; P < 0.02) and had faster labor progress. CONCLUSIONS: Inflammatory cytokines including IL-1ß play a role in cervical ripening. High maternal plasma concentrations of IL-1ß may serve as a marker of advanced cervical ripening and readiness for labor that proceeds with less pain.