The sensitivity of fetal fibronectin (93%) for delivery within 7 days is markedly superior to contraction frequency and cervical dilatation (Table IV). Unlike contractions and dilatation, both of which may occur normally, fetal fibronectin expression is neither normal nor common after 20 weeks. Its presence in cervicovaginal fluid is directly related to the pathophysiologic mechanisms of preterm labor. The positive predictive value for fetal fibronectin of 29% for delivery within 7 days does not look particularly impressive, except in contrast to the poor positive predictive values recorded for cervical dilatation and contraction frequency, emphasizing the need for more accurate means of diagnosis.
The fetal fibronectin test compares favorably with other tests for preterm labor. Mild elevation of maternal C-reactive protein, an acute-phase reactant, has been reported to correlate with likelihood of delivery within 7 days.“-’ In these studies 63% to 85% of women treated for preterm labor whose C-reactive protein level was 20.8 mgidl were delivered within 1 week of presentation compared with only 6% to 29% of women whose C-reactive protein level was ~0.8 mg/dl. Unlike fetal fibronectin, C-reactive protein is not specific for labor and may be increased with any inflammatory condition.