OBJECTIVE: To determine the interrelationship between cervical IL-6, FFN, and other risk factors for SPTB. STUDY DESIGN: All cases (n=125) with SPTB < 32 weeks gestational age (GA) and controls delivered ≥37 weeks (n=125; matched for race, parity, and center) were selected from women enrolled in the NICHD's Preterm Prediction Study. IL-6 concentrations were determined by ELISA in cervical swabs obtained at 220-246 weeks GA. Cutoffs to define an elevated IL-6 included the 90th and 95th percentile for controls (>304.6 and >538.4 pg/ml, respectively). RESULTS: The mean (±SD) IL-6 was significantly higher in cases vs controls (212±339 vs 111±186 pg/ml, p = .008). Using either cutoff, elevated IL-6 was significantly associated with SPTB (90th percentile; 20 vs 9.6%, p=.02 and 95th percentile; 12 vs 4.8%, p = .04). Elevated IL-6 was not significantly associated with bacterial vaginosis (BV), maternal BMI<19.8, or a short cenix (≤25 mm) but was significantly associated with a positive cervicovaginal FFN (90th percentile; OR 5.5, 95% CI 2.6-11.9 and 95th percentile; OR 5.3, 95% CI 2.1-12.9). The mean IL-6 concentration in FFN+ vs FFN- women was 373±406 vs 130±239 pg/ml (p=.001). In a regression analysis adjusting for risk factors significantly associated with SPTB in this population (positive FFN, BMI<19.8, vaginal bleeding in the 1st or 2nd trimester, prior SPTB, short cervix) elevated cervical IL-6 was not independently associated with SPTB (OR 1.8, 95% CI 0.8-4.3). CONCLUSIONS: At 24 weeks, cervical IL-6 is significantly elevated in women who subsequently have SPTB < 32 weeks GA compared to those delivering at term. A positive FFN, but not BV, is strongly associated with elevated cervical IL-6. At 24 weeks, both cervical IL-6 and FFN may be markers for upper genital tract inflammation which later may result in SPTB.