Fetal fibronectin improves the accuracy of diagnosis of preterm labor

OBJECTIVE: Our purpose was to assess the utility of cervicovaginal expression of fetal fibronectin in the diagnosis of preterm labor. STUDY DESIGN: Women seen between 24 and 34 weeksʹ gestation with symptoms of preterm labor, intact membranes, and cervical dilatation <3 cm were enrolled at five university medical centers. Cervicovaginal swabs were obtained and assayed for the presence of fetal fibronectin by means of a monoclonal antibody assay. Results were compared with cervical dilatation and uterine contraction frequency as indicators of interval to delivery and delivery before 37 weeks. RESULTS: A total of 192 eligible women at a mean gestational age of 30.8 ± 2.9 weeks were enrolled from a population of 418 subjects screened. The rate of preterm birth was 32.3% (62/192). The mean interval from presentation to delivery was 25.3 ± 24.1 days in the 45 subjects with a positive fibronectin assay and 52.4 ± 24.8 days in the 147 subjects with a negative assay (p = 0.0001). The sensitivity, specificity, and positive and negative predictive values of fetal fibronectin expression for delivery <37 weeks were 44% (27/62), 86% (112/130), 60% (27/45), and 76% (112/147). The fetal fibronectin assay was especially useful in predicting risk of delivery within 7 days (sensitivity 93% [13/14], specificity 82% [146/178], positive predictive value 29% [13/45], and negative predictive value 99% [146/147]) and was notably superior to both cervical dilatation>1 cm and contraction frequency greater than or equal to eight per hour (sensitivities 29% and 42%, specificities 82% and 67%, positive predictive values 11% and 9%, and negative predictive values 94% and 94%, respectively). CONCLUSION: Cervicovaginal fetal fibronectin predicts delivery within 7 days more accurately than do cervical dilatation and contraction frequency in a population of women evaluated for early preterm labor.