The sensitivity of fetal fibronectin (93%) for delivery within 7 days is markedly superior to contraction fre- quency and cervical dilatation (Table IV). Unlike con- tractions and dilatation, both of which may occur nor- mally, fetal fibronectin expression is neither normal nor common after 20 weeks. Its presence in cervicovaginal fluid is directly related to the pathophysiologic mecha- nisms 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, emphasiz- ing the need for more accurate means of diagnosis.
The fetal fibronectin test compares favorably with other tests for preterm labor. Mild elevation of mater- nal 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 pre- sentation 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.