AMNIOTIC-FLUID INTERLEUKIN-6 AND INTERLEUKIN-8 LEVELS PREDICT THE SUCCESS OF TOCOLYSIS IN PATIENTS WITH PRETERM LABOR

Objective: To determine whether the levels of the cytokines interleukin-6 (IL-6) and IL-8 in amniotic fluid idnetify patients with preterm labor who are resistant to tocolysis. Methods: Amniocenteses were performed in 23 women with documented preterm labor at 20-32 weeks' gestational age who were treated subsequently with tocolytics. The concentrations of IL-6 and IL-8 in amniotic fluid were determined by double-antibody radioimmunoassay methods using recombinant human IL standards. Results: Of the 23 patients, five failed to respond to tocolysis (four delivered within 48 hours), and of the remaining 18, all delivered more than 9 days after tocolysis was initiated (mean 31 +/- 10 days; range 9-61). In women who had failed tocolysis, discriminatory concentrations of IL-6 and IL-8 were 20 and 15 ng/mL, respectively. Of the patients who had amniotic fluid concentrations higher than these thresholds, all failed tocolysis (100% positive predictive value) and delivered within 6 days. The patients with levels below these discriminatory concentrations had successful tocolysis, and 17 of 18 delivered more than 2 weeks after treatment (95% negative predictive value). Conclusion: The success of tocolysis and thus delivery remote from an episode of preterm labor is associated with discriminatory amniotic fluid IL-6 and IL-8 levels of less than 20 and less than 15 ng/mL, respectively. If the immunologic response that causes the release of IL-6 and IL-8 has not occurred, the likelihood of successful tocolysis is extremely high. However, if both IL-6 and IL-8 are elevated, tocolysis is likely to fail and delivery may occur within 48 hours.