In Reply We believe that the evidence supporting the use of fetal fibronectin to screen for the risk of preterm birth in low-risk, asymptomatic women, such as those enrolled in our study, is far from conclusive. Our results indicating a low sensitivity and positive predictive value for fetal fibronectin for the prediction of preterm birth at less than 37 weeks’ gestation are consistent with those from other studies using the same primary outcome in low-risk women. Jwala et al1 evaluated asymptomatic, low-risk women at 18 to 24 weeks’ gestation using a threshold of 5 ng/mL or more of fetal fibronectin and found a sensitivity of 58% and a positive predictive value of 8.75% for predicting preterm birth at less than 37 weeks. Heath et al2 evaluated a cohort of similar women at 23 weeks’ gestation using a threshold of greater than 50 ng/mL and found a sensitivity of 32.6% and a positive predictive value of 8.1% for the prediction of preterm birth at less than 33 weeks. We evaluated 10 000 asymptomatic, low-risk women at multiple time points (6-14 weeks, 16-22 weeks, and 22-30 weeks) using multiple thresholds (≥10 ng/mL, ≥50 ng/mL, and ≥200 ng/mL) and found sensitivities ranging from 2.9% to 34.5% and positive predictive values ranging from 6.4% to 14.0% for the prediction of preterm birth at less than 37 weeks. Our results are consistent with those from 2 other large cohorts of similar low-risk women, which suggests that our methods and conclusions regarding the clinical utility of fetal fibronectin are valid.
Esplin MS, Elovitz M, Iams J. Vaginal Fetal Fibronectin to Predict Spontaneous Preterm Birth—Reply. JAMA. 2017;318(2):199–200. doi:10.1001/jama.2017.7137