Contingent Use of Fetal Fibronectin Testing and Cervical Length Measurement in Women With Preterm Labour

Abstract

ObjectiveTo evaluate the contingent use of fetal fibronectin (fFN) testing and cervical length (CL) measurement to predict preterm delivery, and to validate the use of phosphorylated IGFBP-1 as a predictor of preterm delivery. MethodsWe recruited 71 women with a clinical diagnosis of preterm labour between 24 and 34 weeks, and tested for the presence of fFN and IGFBP-1 in the cervicovaginal secretions of all women immediately before CL measurement. ResultsAmong the 66 women with complete outcome, four were excluded from the final analysis as two had assessment for fFN but no CL measurement, and another two had CL measured but no screening for fFN. Among 62 women with complete results, the mean gestational age at recruitment was 29.4 ± 2.5 weeks. Six women (9.6%) delivered within two weeks of assessment, and 14 (22.5%) delivered before 34 weeks. A positive fFN test resulted in a sensitivity of 83%, a specificity of 84%, a positive predictive value of 36%, and a negative predictive value of 98% for delivery within two weeks; for CL < 25 mm, these figures were 50%, 52%, 10%, and 91%, respectively, and for a positive IGFBP-1, they were 17%, 93%, 20%, and 91%, respectively. A policy of contingent use of fFN (in which the test was assumed to be positive if CL ≤ 15 mm, and fFN was only measured if the CL was between 16 and 30 mm) gave sensitivity, specificity, positive and negative predictive values of 80%, 61%, 17%, and 97%, respectively for delivery within two weeks. Using this contingent use protocol, only one third of women needed fFN screening after CL measurement. ConclusionIn this study, IGFBP-1 screening did not predict preterm delivery and fFN screening provided the best predictive capacity. A policy of contingent use of testing for fFN after CL measurement, or contingent use of CL measurement after fFN screening (depending on available resources) is a promising approach to limit use of resources.