A prospective, double-blinded cohort study using Quantitative fetal fibronectin testing in symptomatic women for the prediction of spontaneous preterm delivery

Background: Quantitative fetal fibronectin (fFN) is under-utilised in Hong Kong. Our objective was to evaluate the effectiveness of quantitative fetal fibronectin (fFN) to predict spontaneous preterm birth in women with symptoms or signs of threatened preterm labour. Methods A prospective, double-blinded cohort study of women with a singleton gestation and with preterm labour symptoms presenting to a tertiary hospital in Hong Kong between 24 + 0 to 33 + 6 weeks was performed from 1st October 2020 and 31st October 2021. Women with vaginal bleeding, ruptured membranes, and cervical dilation > 3 cm were excluded. The primary outcome was spontaneous preterm birth < 37 weeks. Test characteristics of quantitative fFN at different thresholds were evaluated. Results 48 women were recruited. 10 mothers had preterm delivery (< 37 weeks' gestation) and 9 delivered within 48 hours. The NPV to predicting delivery within 14 days is 97.3% using a cut-off of < 50ng/ml and it is 100% when using 10ng/ml as cut-off. On the other hand, using 200 ng/ml as cut-off can also reliably predict women who delivered within 48 hrs– 7 days with PPV of 100%; as well as PTB before gestation 34 weeks and before 37 weeks. Conclusions Quantitative fFN provides different thresholds in addition to the qualitative method (50 ng/mL) to discriminate the risk of preterm delivery in symptomatic women. The high negative predictive value could help clinicians ruling out preterm labour and reducing unnecessary interventions.