Evaluation of a quantitative fetal fibronectin test for spontaneous preterm birth in symptomatic women

OBJECTIVE: The purpose of this study was to determine whether quantification of cervicovaginal fluid fetal fibronectin (fFN) improves diagnostic accuracy of spontaneous preterm birth (sPTB) in symptomatic women. STUDY DESIGN: A prospective blinded predefined secondary analysis of a larger study of cervicovaginal fluid fFN concentration (nanograms per milliliter) in women symptomatic of preterm labor (n =300 women; 22-35 weeks' gestation) with a Hologic 10Q system (Hologic, Marlborough, MA). Clinicians were blinded to the result until after the delivery, but the qualitative Hologic TLIIQ fFN result was made available. RESULTS: The positive predictive value for sPTB (<34 weeks' gestation) increased from 19%, 32%, 61%, and 75% with increasing thresholds (10, 50, 200, and 500 ng/mL, respectively). Compared with <10 ng/mL fFN, the relative risk of delivery was 5.6 (95% confidence interval [CI], 1.05-29.57), 7.9 (95% CI, 1.38-45.0), 22.8 (95% CI, 3.84-135.5), and 51.3 (95% CI, 12.49-211.2; P < .01). CONCLUSION: Quantitative fFN provides thresholds (10 and 200 ng/mL) in addition to the qualitative method (50 ng/mL) to discriminate the risk of sPTB in symptomatic women.