Objective: The common terminal pathway of parturition describes the anatomic, biochemical, endocrine, and clinical events present in the fetus and mother in both term and preterm labor. Labor at term is thought to result from physiologic activation of this pathway, whereas preterm labor is the result of pathologic activating events. The purpose of this study was to determine whether physiologic and pathologic activation could be discerned by the analysis of a cytokine-receptor signaling system. Tumor necrosis factor alpha and its soluble receptors were used as probes because of their pivotal role in the regulation of several processes activated during parturition. Soluble receptors are thought to buffer the biologic and potentially deleterious effects of tumor necrosis factor alpha in pathologic conditions.
Study design: The in vivo concentrations of tumor necrosis factor alpha and its soluble receptors were studied in patients in term labor and preterm labor. Amniotic fluid was retrieved from 175 women and tumor necrosis factor alpha, tumor necrosis factor receptor 1, and tumor necrosis factor receptor 2 concentrations were measured by highly sensitive immunoassays. Patients were classified in the following groups: (1) term labor (n = 29), (2) term not in labor (n = 29), (3) preterm labor leading to term delivery (n = 34), (4) preterm labor without infection resulting in preterm delivery (n = 34), (5) preterm labor with intra-amniotic infection (n = 23), and (6) second trimester (n = 26).
Results: Tumor necrosis factor alpha and tumor necrosis factor receptor 1 concentrations decreased with advanced gestational age (r = -0.51 and r = -0.7; P <.01 for each). (1) Patients in spontaneous term labor had a higher median concentration of tumor necrosis factor alpha than those at term not in labor (median, 6.4 pg/mL; range, 2.4->500 pg/mL vs median, 4.1 pg/mL; range, 1.1-22.7 pg/mL; P <.01) but had lower concentrations of tumor necrosis factor receptor 1 (median, 3.2 ng/mL; range, 1.3-9.1 ng/mL vs median, 4.2 ng/mL; range, 1.6-8.3; P <.001) and tumor necrosis factor receptor 2 (median, 5.5 ng/mL; range, 0.73-12.8 ng/mL vs median, 6.8 ng/mL; range, 2.9-12.9 ng/mL; P <.01). (2) In contrast, patients with preterm labor leading to preterm delivery had higher concentrations of tumor necrosis factor alpha (median, 12.3 pg /mL; range, 1.5->500 pg/mL vs median, 4.8 pg/mL; range, 1-60.9 pg/mL; P <.01), tumor necrosis factor receptor 1 (median, 8.8 ng/mL; range, 2.5-38 ng/mL vs median, 6.2 ng/mL; range, 1.4-28 ng/mL; P <.05), and tumor necrosis factor receptor 2 (median, 8.5 ng/mL; range, 3.5-45.4 ng/mL vs median, 6.1 ng/mL; range, 1.99-14.1 ng/mL; P <.01) than patients with preterm labor who delivered at term. (3) Microbial invasion of the amniotic cavity was associated with dramatic increases in the concentrations of tumor necrosis factor alpha (median, 93.5 pg/mL; range, 1.2->500 pg/mL) and its soluble receptors tumor necrosis factor receptor 1 (median, 8.8 ng/mL; range, 2.1-36.7 ng/mL) and tumor necrosis factor receptor 2 (median, 11.8 ng/mL; range, 3.4-46. 3 ng/mL), concentrations that were significantly higher than in those with preterm labor who delivered at term and those who delivered preterm but were not infected.
Conclusion: The tumor necrosis factor alpha and tumor necrosis factor alpha soluble receptor profiles are different in term and preterm parturition. Our observations provide support for the thesis that preterm parturition is a pathologic condition. Increased tumor necrosis factor alpha soluble receptor concentrations may attenuate the deleterious effects of the excess of tumor necrosis factor alpha found in pathologic labor.