Fetal fibronectin as a predictor of spontaneous preterm labour in asymptomatic women with a cervical cerclage

Objective  To assess the accuracy of fetal fibronectin (fFN) testing for prediction of preterm labour in asymptomatic high-risk women with a cervical cerclage.
Design  Retrospective observational study.
Setting  United Kingdom.
Population  Nine hundred and ten asymptomatic women at high-risk of Preterm birth referred to specialist antenatal clinics and undergoing fFN testing between November 1997 and December 2007.
Methods  Women had fFN tests taken between 23⁺⁰ and 27⁺⁶ weeks' gestation, on one or more occasions.
Main outcome measures  Sensitivity, specificity, positive predictive values and negative predictive values of fFN testing for predicting delivery <30 and <37 weeks were compared in those with and without cerclage.
Results  For delivery <30 weeks' gestation, the specificity of fFN testing was significantly lower in women with cervical cerclage (77% vs 90%; P  ≤ 0.00001). The sensitivity of the test was similar between the groups (78.6 (no-cerclage) vs 60% (cerclage); P  > 0.4). The negative predictive value of the fFN test for delivery <30 weeks was high in both groups (>98%).
Conclusions  Asymptomatic high-risk women with cerclage in situ are more likely to have a false positive fFN test. The negative predictive value is similar.