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PF.08 Quantitative Fibronectin Can Be Used For Earlier Prediction of Preterm Birth from 18 Weeks, But the Positive Threshold Needs Redefining
  1. NL Hezelgrave,
  2. DS Abbott,
  3. SK Radford,
  4. P Seed,
  5. R Tribe,
  6. AH Shennan
  1. Division of Women’s Health KCL, Women’s Health Academic Centre, KHP, London, UK

Abstract

Introduction Fetal fibronectin (fFN) is an excellent predictor of spontaneous preterm birth (sPTB) and is used qualitatively (<50 ng/ml negative threshold) from 22 weeks gestation. Its value at earlier gestations using a quantitative test (qfFN) is unknown.

Methods A prospective secondary analysis of 431 asymptomatic women at high risk of sPTB, who underwent qfFN testing at 18–21 + 6 weeks. 327 women underwent later testing at 22–26 + 6 weeks (acting as their own controls). The end-points were sPTB/preterm premature rupture of membranes and delivery before 30, 34 and 37 weeks gestation and within 8 weeks of testing.

Results Early qfFN predicted delivery within 8 weeks of testing, <30, <34 and <37 weeks with receiver operating characteristics (ROC) areas of 0.66 (0.54–0.80, p < 0.05), 0.68 (0.56–0.79, p < 0.01), 0.68 (0.58–0.78 p < 0.001) and 0.64 (0.57–0.72, p < 0.001). 22-week test prediction was ROC areas of 0.77 (0.63–0.91 p < 0.001), 0.78 (0.61–0.95, p < 0.001) and 0.79 (0.70–0.89, p < 0.001) respectively. A qFFN result of <10 ng/ml at earlier gestations had only 1%, 2% and 4.3% of women delivered within 8 weeks, <30 and <34 weeks gestation, rising to 6.7%, 8.1% and 14.1% with values between 10–49.9 ng/ml (all differences statistically significant, p = 0.03, 0.02, 0.004 by Fishers-Exact). The 22-week test had 1.0%, 1.0% and 2% respectively, rising to 6.7%, 3.3% and 14% with values between 10–49.9 ng/ml (p = 0.02, 0.23, 0.004).

Conclusion qfFN is valid for screening for sPTB at 18 weeks, but has inferior predictive value to 22 weeks. Early identification may enable earlier targeted management. A threshold of <10 ng/ml is more appropriate than current practise to define low risk at 18 weeks.

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