The relationship between amniotic fluid interleukin-6 concentration and histologic evidence of chorioamnionitis

Background. Chorioamnionitis is considered to be one of the important causes of preterm labor. To investigate the relationship between inflammatory cytokines in amniotic fluid and the histologic evidence of chorioamnionitis, we studied amniotic fluid interleukin-6 (IL-6) levels in patients with preterm labor. Methods. Between 1993 and 1996, we obtained amniotic fluid by amniocentesis from 110 patients before 32 weeks of gestation who had preterm labor on admission. We measured IL-6 levels in the amniotic fluid with an ELISA method. Histologic examination of placentae and fetal membranes after delivery was evaluated. As controls, we measured IL-6 levels in the amniotic fluid of 37 patients without preterm labor. Seventy-eight patients delivered after 35 weeks of gestation, and 32 patients delivered before 34 weeks of gestation. Analysis was conducted using Mann-Whitney U test and Scheffe's multiple comparison test. Results. Amniotic fluid IL-6 levels in patients delivering before 34 weeks were significantly higher than those in patients delivering after 35 weeks (p<0.01), IL-6 levels in the amniotic fluid were significantly different among control patients, patients without chorioamnionitis and those with histologic stages I, II and III which means subchorionic intervillositis, chorionitis and amnionitis, respectively (controls vs patients with stage I, II, III: p<0.001, patients without chorioamnionitis vs those with stage II, III, stage I vs II, stage II vs III: p<0.01). The IL-6 concentration in the amniotic fluid associated with histologic stages II or III was above 3500 pg/ml (sensitivity: 87.5%, specificity: 89.5%). Conclusions. Our findings indicate that amniotic fluid IL-6 may have a sensitive diagnostic and prognostic value in the management of preterm labor and is an index of the severity of chorioamnionitis during pregnancy.