Vaginal fetal fibronectin as a predictor of spontaneous preterm delivery in the patient with cervical cerclage

OBJECTIVE: The purpose of this study was to assess the validity of vaginal fetal fibronectin as a screening test for spontaneous preterm birth in patients with cervical cerclage. STUDY DESIGN: A historic cohort of 117 patients who underwent cervical cerclage placement between 1996 and 2002 were identified. All patients were followed up in a maternal-fetal medicine faculty practice in a university setting. Serial fetal fibronectin samples of vaginal secretions were collected every 2 to 3 weeks, starting at 22 weeks of gestation and continuing until 32 weeks or delivery, whichever came first. RESULTS: There were 81 singleton, 23 twin, 12 triplet, and 1 quadruplet pregnancies. There were 61 ultrasound-indicated, 47 prophylactic, and 9 emergency cerclages that were placed. Most cerclages were of the modified Shirodkar type (95%), with a median gestational age at cerclage placement of 16.6 weeks. Overall, 33.3% of gestations were delivered spontaneously before 37 weeks of gestation; 17.1% of gestations were delivered spontaneously before 34 weeks. For deliveries within 2 weeks and 3 weeks of a single fetal fibronectin assessment, the test had a sensitivity of 50% and 48.3%, a specificity of 90% and 91.1%, a positive predictive value of 16.3% and 28.6%, and a negative predictive value of 97.9% and 96%, respectively. Subgroup analysis by number of fetuses (singleton, twin, and higher order multiple gestations) revealed similar values. For delivery before 34 weeks of gestation, fetal fibronectin had a sensitivity of 50%, a specificity of 78.4%, a positive predictive value of 33.3%, and a negative predictive value of 88%. CONCLUSION: This study is the first to evaluate the use of vaginal fetal fibronectin assessments to screen for preterm birth in patients who had undergone cervical cerclage procedures. We conclude that this test has similar validity to predict spontaneous preterm delivery in these high-risk pregnancies, as in previously published cohorts.