A single cervical fetal fibronectin screening test in a population at low risk for preterm delivery: an improvement on clinical indicators?

OBJECTIVE: To assess the accuracy of a single cervical fetal fibronectin test to predict spontaneous preterm delivery in an unselected antenatal population.

DESIGN: A prospective blind cohort study.

SETTING: Antenatal clinic of a teaching hospital in a Brussels semiurban area.

PARTICIPANTS: An unselected group of 170 women followed at the antenatal clinic.

METHODS: A single cervical sample was obtained between 24 and 33 completed weeks of pregnancy. The fibronectin test was compared with clinical evaluation and their predictive properties were assessed.

RESULTS: Fifteen women were excluded from the analysis because of elective preterm delivery for medical indications or loss to follow up. Of the 155 remaining women, nine (7%) had a spontaneous preterm delivery. For a single fetal fibronectin test, the sensitivity was 26.7%, the specificity 95.7%, and the positive and negative predictive values 40.0% and 92.4%, respectively. The likelihood ratio of a positive was similar to that of clinical predictors of preterm birth (LR = 6.2; 95% CI 2.0-19.6). Sensitivities were low for both clinical criteria and the fetal fibronectin test.

CONCLUSIONS: Because of low sensitivity in a low risk population, screening for preterm delivery should not be based on the result of a single fetal fibronectin test alone. However, due to its high specificity the test might be useful in avoiding unnecessary medical intervention.