The frequency and clinical significance of intra-amniotic inflammation in patients with a positive cervical fetal fibronectin

OBJECTIVE: A positive fetal fibronectin result in cervicovaginal fluid is a powerful predictor of preterm delivery and is considered a marker for upper genital tract infection (ie, intrauterine infection). Treatment with antimicrobial agents is being considered in patients with a positive fetal fibronectin test of cervico/vaginal fluid. This study was undertaken to determine the frequency and clinical significance of intra-amniotic infection/inflammation in patients with a positive fetal fibronectin. STUDY DESIGN: A total of 1709 pregnant women (gestational age, 23-31 weeks) were screened for cervical fetal fibronectin. Patients with a positive fibronectin were offered amniocentesis for the diagnosis of intra-amniotic infection and treatment with antibiotics. Amniocentesis was performed in 58 patients with a positive fibronectin test (>50 ng/mL). Amniotic fluid was cultured for aerobic/anaerobic bacteria and mycoplasmas. Polymerase chain reaction assay for Ureaplasma urealyticum was performed. Interleukin-6 concentrations were measured by a specific immunoassay. Nonparametric statistics were used for analysis. RESULTS: None of the patients with a positive fibronectin had a positive amniotic fluid culture. U urealyticum was detected in 1 case (1.8%) with the polymerase chain reaction assay. Amniotic fluid IL-6 was elevated (>2.5 ng/mL) in 5.3% of patients (3/57 patients); all of these patients delivered preterm neonates. There was no relationship between amniotic fluid IL-6 and cervical fibronectin concentration (r = 0.14; P > .1). Patients who delivered preterm (<34 weeks) had higher median amniotic fluid IL-6 and cervical fetal fibronectin concentrations than those patients who delivered after 34 weeks (IL-6: median, 2.1 ng/mL [range, 0.1-25.3 ng/mL] vs median, 0.3 ng/mL [0.03-2.4 ng/mL]; P < .05; fibronectin: median, 509 ng/mL [260->1000 ng/mL] vs median, 155 ng/mL [50-889 ng/mL]; P < .01). CONCLUSION: Intra-amniotic infection was detected in 1.8% of cases with a positive fibronectin in the cervical fluid; intra-amniotic inflammation was present in 5.3% of cases. All patients with a positive fetal fibronectin and intra-amniotic inflammation delivered preterm neonates.