Clinical Question

Does testing for fetal fibronectin in patients with signs and symptoms of preterm labor help to prevent preterm birth (i.e., birth before 37 weeks' gestation)?

Evidence-Based Answer

Fetal fibronectin testing may reduce preterm birth, although the evidence is not strong enough to recommend regular testing. Knowing the results of fetal fibronectin testing does not lead to a reduction in secondary outcomes such as preterm birth before 34 weeks' gestation, admission to the neonatal intensive care unit, or perinatal death.¹ (Strength of Recommendation: B, based on inconsistent or limited-quality patient-oriented evidence.)

Practice Pointers

Preterm birth affects about one in 10 births in the United States and is the second most common cause of infant mortality.^2,3 Tools to identify the risk of preterm birth are limited. One potential marker, fetal fibronectin, is a glycoprotein produced by amniocytes and cytotrophoblasts and is found at the maternal-fetal interface. It is believed that fetal fibronectin keeps the amniotic sac attached to the uterine lining. In practice, a positive test result indicates that the mother is at increased risk of preterm birth during the ensuing seven days.⁴ This review focuses on the potential of fetal fibronectin testing to prevent preterm birth in patients with signs and symptoms of preterm labor.

The authors assessed six trials with 546 women who had a singleton pregnancy and signs and symptoms of preterm labor at 23 weeks' to 34 6/7 weeks' gestation.¹ Only studies evaluating outcomes based solely on fetal fibronectin test results were included. Interventions based on additional methods of preterm delivery prediction, such as cervical length measurement, were not included. One trial was completed in the United Kingdom, and five were completed in the United States.

Management of preterm labor based on fetal fibronectin results did not reduce the overall rate of preterm birth (relative risk = 0.72; 95% CI, 0.52 to 1.01). However, when excluding one of the smallest trials (n = 77), which was called into question based on unclear risk of allocation concealment, fetal fibronectin results appeared to significantly reduce the risk of preterm birth (relative risk = 0.67; 95% CI, 0.46 to 0.97), leading authors to suggest that there may be a benefit from fetal fibronectin testing.

Fetal fibronectin testing results did not affect any of the secondary outcomes, including preterm birth at less than 34 weeks' gestation, gestational age at delivery, perinatal death, maternal hospitalization, tocolysis, use of steroids for fetal lung maturity, neonatal intensive care unit admission, or maternal well-being.

This review was limited to studies using only fetal fibronectin testing. In clinical practice, fetal fibronectin results would not be used alone. The clinician would likely seek additional information such as a thorough history and cervical length. A lack of demonstrable change in secondary outcomes also indicates that fetal fibronectin testing alone should not change management.

A 2016 American College of Obstetricians and Gynecologists practice bulletin notes that although fetal fibronectin and cervical length may predict preterm birth, there is no evidence to support the use of these measures to guide management of preterm labor.⁵ Further studies are needed to determine if fetal fibronectin testing can lead to prevention of preterm birth. Physicians may consider fetal fibronectin testing in patients with signs and symptoms of preterm labor to aid in predicting the risk of preterm birth.

The practice recommendations in this activity are available at http://www.cochrane.org/CD006843.