Amniotic fluid levels of immunoreactive monocyte chemotactic protein-1 increase during term parturition

Parturition is characterized by an influx of inflammatory cells into gestational tissues, a phenomenon conducive to increased myometrial contractility, cervical ripening and decidual/membrane activation. Monocyte chemotactic protein-1 (MCP-1), a potent chemoattractant and activator of monocytes/macrophages, is expressed in gestational tissues and, thus, may participate in the final common pathway of labor. This study was undertaken to determine whether the amniotic fluid concentrations of immunoreactive MCP-1 are altered with gestational age or spontaneous labor at term with and without prelabor rupture of the gestational membranes. We also sought to identify intrapartum differences in the concentrations of immunoreactive MCP-1 between the upper and lower amniotic fluid compartments.

A cross-sectional study was conducted to assess the concentrations of immunoreactive MCP-1 in amniotic fluid. Amniotic fluid samples were obtained from 225 women as follows: (1) women undergoing mid-trimester (14-18 weeks of gestation) amniocentesis for genetic indications, whose pregnancy outcome was normal (n = 84); (2) women in labor (n = 52) and not in labor (n = 31) at term, with intact gestational membranes; (3) women with rupture of the gestational membranes in labor (n = 18) and not in labor (n = 26), at term; and (4) women in labor at term for whom paired amniotic fluid samples were obtained through transvaginal and transabdominal amniocenteses (n = 14). Immunoreactive MCP-1 was assessed with a specific and sensitive immunoassay that had been validated for amniotic fluid. Non-parametric statistics were used for analysis.

Immunoreactive MCP-1 was detected in all amniotic fluid samples. Spontaneous human parturition was associated with a significant increase in the amniotic fluid concentrations of immunoreactive MCP-1 (not in labor: median 595 pg/ml, range 183-3579 pg/ml vs. in labor: median 862 pg/ml, range 183-9609 pg/ml; p = 0.01). The median amniotic fluid concentrations of immunoreactive MCP-1 were significantly higher in the lower amniotic fluid compartment than in the upper amniotic fluid compartment (lower compartment: median 2913 pg/ml, range 1360-17080 pg/ml vs. upper compartment: median 1603 pg/ml, range 1070-8062 pg/ml; p = 0.004.). Spontaneous rupture of the gestational membranes at term was not associated with a significant change in the amniotic fluid concentrations of immunoreactive MCP-1.

Immunoreactive MCP-1 is a physiological constituent of the amniotic fluid. The amniotic fluid levels of immunoreactive MCP-1 increase during spontaneous labor at term. A topographic difference in the concentration of immunoreactive MCP-1 was observed in the amniotic cavity, with higher concentrations being noted in the lower amniotic fluid compartment, as compared with the upper amniotic fluid compartment. These findings support the hypothesis that MCP-1 may play a role in the final common pathway of spontaneous labor.