Prediction of spontaneous preterm birth by fetal fibronectin and uterine activity

To evaluate the usefulness of fetal fibronectin and home uterine contraction assessment in predicting preterm birth (before 34 weeks) in at-risk asymptomatic women. One hundred fifty women were enrolled prospectively; five were lost to follow-up, leaving 145 women available for analysis. Because patients with preterm labor before 34 weeks' gestation most commonly develop this problem after 28 weeks, the period of 26–28 weeks' gestation was selected prospectively as the first window for prediction and study analysis. Eighty-five of 145 asymptomatic women at high risk for preterm birth had both home uterine contraction assessment of 2 hours per day and one or more cervical sampling(s) for fetal fibronectin measurement at 26–28 weeks. A positive home uterine contraction assessment was defined as contractions exceeding two per hour averaged over the 2-week study interval. Positive fetal fibronectin was defined as greater than 50 ng/mL. Fourteen of the 85 women (16.5%) delivered before 34 weeks. Home uterine contraction assessment alone had a sensitivity, specificity, positive predictive value, and negative predictive value for preterm birth of 64, 85, 45, and 92%, respectively; fetal fibronectin alone was associated with values of 43, 89, 43, and 89%, respectively. A positive home uterine contraction assessment was associated with a relative risk (RR) for preterm birth of 5.9 (95% confidence interval [CI] 2.4–14.2), whereas a positive fetal fibronectin demonstrated an RR of 3.8 (95% CI 1.5–9.4). When both assessments were positive, all patients delivered before 34 weeks and there was an RR of 27.0 (95% CI 8.7–84.1) compared with those with both tests being negative. Only two patients with both tests negative delivered before 34 weeks (negative predictive value 96%). Both the home uterine contraction assessment and fetal fibronectin accurately predicted preterm birth before 34 weeks. When both tests were combined, the predictive ability improved substantially.