OBJECTIVE:To determine whether the risk of intra-amniotic infection, intra-amniotic inflammation, and spontaneous preterm delivery varies as a function of the concentration of cervical fetal fibronectin in patients presenting with preterm labor and intact membranes. STUDY DESIGN: This was a prospective study in which patients with preterm labor and intact membranes had a sample collected for quantitative cervical fetal fibronection at the time of admission. Patients underwent amniocentesis for the assessment of the microbial state of amniotic cavity. Amniotic fluid was cultured for aerobic and anaerobic bacteria and for genital mycoplasmas. Intra-amniotic inflammation was defined as an elevated amniotic fluid matrix metalloproteinase-8 (MMP-8) concentration (> 23 ng/mL). The quantitative fetal fibronectin concentration in cervical secretions was determined with a commercially available enzyme-linked immunosorbent assay. Nonparametric tests and survival techniques were used for analysis. RESULTS: A total of 180 patients were enrolled in the study. 1) The prevalence of intra-amniotic infection, intra-amniotic inflammation, the combination of intra-amniotic infection or inflammation and spontaneous preterm delivery within 7 days were 7.3% (13/179), 30% (54/180), 32.2% (58/180) and 33.9% (61/178), respectively; 2) The higher the fetal fibronectin concentration, the greater the risk of intra-amniotic infection, intra-amniotic inflammtion, intraamniotic infection and/or inflammation and spontaneous preterm delivery within 7 days (P<0.005 for intra-amniotic infection and P<0.001 for intra-amniotic inflammation and infection and/or inflammation); 3) A high concentration of fetal fibronectin in cervical fluid was associated with spontaneous preterm delivery within 7 days and 14 days only in patients without intra-amniotic infection and/or inflammation; 4) Among the patients with a fetal fibronectin < 50 ng/mL, intra-amniotic infection and/or inflammation was identified in 7.6% (6/79) of patients and 66.7 % (4/6) delivered within 7 days of amniocentesis. CONCLUSION: 1) the higher the concentration of cervical fetal fibronectin, the greater the risk of intra-amniotic infection and/or inflammation and spontaneous preterm delivery in patients with preterm labor and intact membranes; 2) Intra-amniotic infection and/or inflammation was identified in 7.6% of patients with a fetal fibronectin concentration of lower than 50 ng/ml.