Objectives This study investigated the potential for fFN to predict PTB in high-risk asymptomatic women from 18 weeks gestation, earlier than fFN has been previously used clinically.

Study design A prospective observational study of 113 high-risk asymptomatic participants that were recruited through St. Thomas' hospital high-risk antenatal clinics, the preterm surveillance clinic, the antenatal ward and the antenatal day assessment unit. Participants acted as their own controls and had tests taken between 18-22 weeks and within the standard testing period of 22-35 weeks. Outcome measures were spontaneous delivery before 30, 34 and 37 weeks gestation and within 8 weeks of conducting the test.

Results fFN samples taken from 18 weeks showed a strong and significant predictive value for the prediction of PTB at all end-points (Table 1) with the strongest predictive value being for delivery before 30 weeks gestation. fFN sampled between 18-22 weeks was equivalent to tests taken beyond 22 weeks in the standard testing period. Both testing periods produced 100% sensitivity, 82% specificity and receiver operator characteristics (ROC) areas above 0.9.

Conclusion fFN screening is valid for the prediction of PTB from 18 weeks in high-risk asymptomatic women allowing for earlier identification and targeted management.