Background The presence of raised fetal fibronectin (fFN) levels in cervicovaginal secretions between 24–34 weeks gestation is associated with an increased risk of spontaneous preterm birth in symptomatic women. Recent developments in testing now enable a quantitative level to be derived. Currently, a level of ≥50 µmol/l is considered a positive test result. Presently, there is no data to guide clinicians as to which levels signify greater or lesser risk of imminent delivery.

Method This retrospective study was undertaken within Leeds Teaching Hospitals Trust. All fFN tests undertaken in the Maternity Assessment Unit between August 2010 and July 2012 were ascertained, and pregnancy outcomes were collated. 303 results had adequate data to allow analysis and 97 of these included quantitative fFN levels.

Results The overall sensitivity of the test in predicting delivery within 14 days of the test was 64.3%, with a positive predictive value of 17.3%. The specificity of the test was 85.1%, with a negative predictive value (NPV) of 98.0%. The test was more reliable when used in gestations ≤29 weeks when compared to those ≥ 30 weeks as higher values were obtained for specificity and sensitivity; 85.8% and 100% respectively. When examining the quantitative data, the percentage of ladies who delivered within 14 days from the test was 3% if fFN levels were between 0–19, 20% (20–49), 0% (50–199), 20% (200–499) and 100% (>500).

Conclusion Knowledge of quantitative fFN levels may enable more accurate risk assessment of symptomatic women at risk of preterm birth, and inform follow-up pathways.