To compare quantitative fetal fibronectin measurement from 18 to 21 weeks of gestation to measurement at 22–27 weeks of gestation for the prediction of spontaneous preterm birth.METHODS:
In a prospective cohort study, we studied the accuracy of cervicovaginal fluid quantitative fetal fibronectin concentrations measured between 18 0/7 weeks of gestation and 21 6/7 weeks of gestation in high-risk asymptomatic women to predict spontaneous preterm birth before 34 weeks of gestation. Predefined fibronectin thresholds were 10 or greater, 50 or greater, and 200 ng/mL or greater. Diagnostic accuracy of the early test (n=898) was compared with the standard test performed between 22 0/7 and 27 6/7 weeks of gestation (n=691) in the same cohort. Subgroup analysis was performed according to cervical length measurement.RESULTS:
Of 898 women, 8.7% delivered spontaneously before 34 weeks of gestation. Only 3.8% of the women with concentrations less than 10 ng/mL (65% of test results) delivered before 34 weeks of gestation. A concentration threshold of 10 ng/mL measured at 18 and 22 weeks of gestation had comparably high sensitivity (early 0.71, 95% confidence interval 0.60–0.81; standard 0.76, 0.63–0.87) and negative predictive value (early 0.96, 0.94–0.98; standard 0.97, 0.95–0.99) for delivery before 34 weeks of gestation. Specificity was also comparable (early 0.69, 0.65–0.72; standard 0.70, 0.66–0.74). A threshold of 200 ng/mL had high specificity (early 0.96, 0.94–0.98; standard 0.96, 0.94–0.97) with lower sensitivity (early 0.26, 0.17–0.37; standard 0.35, 0.22–0.49). Consideration of cervical length strengthened prediction.CONCLUSION:
Quantitative cervicovaginal fetal fibronectin measured from 18 to 21 weeks of gestation has similar predictive value as measurement at 22–27 weeks of gestation for prediction of spontaneous preterm birth. Low fibronectin concentrations are associated with spontaneous preterm birthrates approaching population background levels.