Will cervicovaginal interleukin-6 combined with fetal fibronectin testing improve the prediction of preterm delivery?

OBJECTIVE: We sought to investigate if determination of cervicovaginal interleukin-6 (IL-6) levels would enhance the positive predictive value of fetal fibronectin (fFN) for preterm birth. METHODS: A prospective cohort study was undertaken of 135 women between 24 and 34 weeks gestation with symptoms of suspected preterm labor. Cervicovaginal secretions were collected for both IL-6 and fFN and measured by immunoassay and ELISA, respectively. Outcome variables included preterm delivery in less than 48 h, within 7 days, and prior to 37 weeks. Statistical analysis was performed with Fisher's exact test, regression for logarithmic transform levels, and multivariate logistic regression. ROC curves were created for IL-6 levels. RESULTS: IL-6 and fFN levels were both elevated in cervicovaginal secretions of women with symptoms of preterm labor. IL-6 values >100 pg/ml resulted in a odds ratio for delivery at <37 weeks of 1.57 (95%CI=0.89-2.75, P=.11), whereas fFN values >50 ng/ml resulted in a preterm delivery risk of 4.58 (95%CI=1.54-13.35, P=.003). Combining IL-6 and fFN results did not improve upon the predictive value of fFN alone for preterm birth [odds ratio 4.00 (95%CI=1.31-12.17, P=.015)]. CONCLUSION: Cervicovaginal IL-6 levels did not provide any additional, independent effect on the prediction of preterm birth beyond that of fFN testing alone.