Value of fetal fibronectin as a predictor of preterm delivery for a low-risk population

Objective: We examined clinical value of cervical fetal fibronectin detection by a quantitative enzyme-linked immunosorbent assay as a predictor of preterm delivery in a population (n=111) of middle-class pregnant women considered to be at low risk for preterm delivery. Study Design: In this prospective study, fetal fibronectin samples from cervicovaginal secretions were obtained biweekly from 24 to 34 weeksʹ gestation. Results: Twenty-two (20%) patients had at least one positive fetal fibronectin test result. Eleven women (10%) were delivered spontaneously at <37 weeks; seven of these had at least one positive fetal fibronectin test result (positive predictive value=31.8%, sensitivity=63.6). An additional three women were delivered prematurely because of other obstetric indications, and all had negative fetal fibronectin test results. The remaining 15 patients with at least one positive fetal fibronectin test result were delivered at term (≥37 weeks). Of the seven women with positive fetal fibronectin results who were delivered prematurely, five were delivered within 2 weeks of obtaining a positive result. However, there were no obvious clinical discriminators between true-positive and false-positive fetal fibronectin results. Eighty-nine women tested negative, and 85 of these women were delivered at term (specificity=82.0%). The negative predictive value of fetal fibronectin as a predictor of term delivery in this low-risk population is 96.6%, with odds ratio=8.8 (95% confidence interval 1.9 to 40.3), relative risk=6.9 (95% confidence interval 1.8 to 26.6) and Fisher Exact Test p=0.007. Conclusions: Although negative biweekly fetal fibronectin determinations for prediction of preterm delivery in this low-risk obstetric population correlate well with the absence of preterm delivery, they are of limited clinical value for the prediction of preterm birth.