From the Guidelines
Repeating a fetal fibronectin (FFN) test after a positive result two weeks ago is generally not recommended. The clinical implications of a positive result have not been evaluated fully because no intervention has been shown to decrease the risk of preterm delivery, as stated by the American College of Obstetricians and Gynecologists in 2002 1. Once a positive FFN result has been obtained, subsequent testing within 2-3 weeks provides limited additional clinical value because the protein can remain detectable for several weeks after release.
The initial positive result already indicates an increased risk of preterm birth within the next 7-14 days. However, it's essential to note that many women with positive FFN results do not deliver preterm. Management should focus on clinical assessment, including:
- Monitoring for symptoms of preterm labor
- Cervical length measurement by ultrasound, which is a reliable and reproducible way to assess the length of the cervix, as shown in prospective trials 1
- Potentially initiating interventions such as corticosteroids for fetal lung maturity if preterm birth appears imminent
The FFN test is most useful as a negative predictor - a negative result has a high chance of no delivery within the next week, allowing clinicians to avoid unnecessary interventions. If clinical concerns persist beyond 2-3 weeks after the initial positive test, a new clinical assessment should guide management rather than repeat FFN testing. This approach prioritizes the patient's morbidity, mortality, and quality of life by avoiding unnecessary tests and interventions.
From the Research
Repeating a Positive Fetal Fibronectin (FFN) Test
- The decision to repeat an FFN test after a positive result over two weeks ago should be based on the clinical context and the patient's individual risk factors for preterm labor 2, 3, 4.
- Studies have shown that a positive FFN test is associated with an increased risk of preterm birth, but the predictive value of the test decreases over time 4, 5.
- The sensitivity and specificity of FFN testing for predicting preterm birth vary depending on the population being studied and the gestational age at testing 2, 3, 4.
- In patients with a cervical cerclage, FFN testing has been shown to be a valid diagnostic tool for evaluating preterm labor, but the test's performance characteristics may be affected by the presence of a cerclage 2, 3, 4.
Factors to Consider When Deciding to Repeat an FFN Test
- The patient's individual risk factors for preterm labor, such as a history of preterm birth or cervical insufficiency 6.
- The gestational age at the time of the initial positive FFN test and the current gestational age 4, 5.
- The results of other diagnostic tests, such as cervical length measurement, and the patient's clinical symptoms 5.
- The potential benefits and risks of repeating the FFN test, including the possibility of false positive or false negative results 3, 4.
Clinical Guidelines and Recommendations
- The American College of Obstetricians and Gynecologists and other professional organizations have published guidelines for the diagnosis and management of preterm labor, but these guidelines do not specifically address the issue of repeating an FFN test after a positive result 6.
- Clinical judgment and individualized decision-making are essential when determining whether to repeat an FFN test in a patient with a history of a positive result 2, 3, 4.