A Cochrane review included 5 trials involving a total of 474 women. Preterm birth less than 37 weeks was significantly decreased with management based on knowledge of foetal fibronectin (FFN) results compared to controls without such knowledge (15.6% vs 28.6%; RR 0.54, 95% CI 0.34 to 0.87, 3 trials, n=275). All other outcomes for which there were available data (preterm birth at less than 34, 32, or 28 weeks; gestational age at delivery; birthweight less than 2500 grams; perinatal death; maternal hospitalization; tocolysis; steroids for fetal lung maturity; and time to evaluate) were similar in the two groups. No other maternal or neonatal outcome was available for meaningful analysis.
A systematic review including 27 studies with a total of nearly 20 000 women was abstracted in DARE. Foetal fibronectin had a high specificity (83%) but a rather low sensitivity (61%) for preterm delivery occurring < 34 weeks gestation. The sensitivity of the test in predicting those delivering < 37 weeks is even lower. The sensitivity of foetal fibronectin is highest at >= 7 days before delivery (76%), and declines with increasing intervals to 43% at 28 days.
Comment: The quality of evidence is downgraded by imprecise results, by inconsistency (heterogeneity in interventions and outcomes), by indirectness (lack of data on clinically important outcomes).