Accuracy of fetal fibronectin for assessing preterm birth risk in asymptomatic pregnant women: a systematic review and meta-analysis.
Fetal fibronectin (fFN) is a validated test for assessing risk of preterm birth for women presenting with symptoms. Our aim was to evaluate the accuracy of fFN to detect the risk of preterm birth in asymptomatic women. Searches were conducted to identify studies where fFN was performed in asymptomatic women beyond 22 weeks' gestation. EMBASE, MEDLINE, CINHAL, AMED and BNI were searched between 2005 and 2017. Studies before 2005 were identified from a published systematic review. Women were grouped as singleton pregnancies, with and without risk factors for preterm birth, and multiple pregnancy. Quality assessment was performed using QUADAS-2. When possible, data were pooled using a hierarchical, bivariate random effects model. Fifteen studies met the inclusion criteria: six studies of singleton pregnancies in women without risk factors (1236 women), four in women with risk factors for preterm birth (2628 women) and five studies were of multiple pregnancy (1427 women). The pooled sensitivity and specificity of fFN in "no risk factors singletons" were 0.48 (95% CI 0.20-0.77), and 0.96 (95% CI 0.86-0.99), respectively. The likelihood ratio of a positive test result was 12 (95% CI 4.70-30.68). The pooled sensitivity and specificity of fFN in "risk factors singletons" were 0.34 (95% CI 0.24-0.43), and 0.91 (95% CI 0.88-0.93). The accuracy of fFN in multiple pregnancies was inconclusive. Our findings suggest in asymptomatic singleton pregnancies without risk factors, a positive fFN result indicates a large shift from pre- to post-test probability, possibly identifying women at increased risk of preterm birth.