From the Guidelines
Fetal fibronectin testing is indicated in pregnant women between 24 and 34 weeks gestation who present with symptoms of preterm labor, as it has a high negative predictive value, allowing clinicians to avoid unnecessary interventions. Fetal fibronectin (fFN) is a glycoprotein produced by the fetal membranes that acts as a biological glue, helping to secure the placental membranes to the uterine lining. The test is most valuable when the result is negative, as it has a high negative predictive value (>99%), meaning that women with a negative result have less than a 1% chance of delivering within the next 7-14 days, as noted in studies such as 1.
Key Points to Consider
- The test should not be performed if there is rupture of membranes, cervical dilation >3 cm, or recent sexual intercourse or cervical examination (within 24 hours), as these can cause false positive results.
- A positive result (>50 ng/mL) indicates an increased risk of preterm birth but is less predictive.
- The test involves collecting cervicovaginal secretions during a speculum examination and can provide results within an hour, making it useful for immediate clinical decision-making in the management of threatened preterm labor, as supported by guidelines and recommendations from organizations such as those discussed in 1.
Clinical Decision Making
When deciding whether to order a fetal fibronectin test, clinicians should consider the patient's symptoms and medical history, as well as the potential benefits and limitations of the test. The test can help identify women at low risk of preterm birth, allowing for more targeted interventions and reducing unnecessary hospitalizations and treatments. However, it is essential to interpret the results in the context of the patient's overall clinical presentation, as noted in 1.
From the Research
Definition and Purpose of Fetal Fibronectin
- Fetal fibronectin (FFN) is an extracellular matrix glycoprotein localized at the maternal-fetal interface of the amniotic membranes, between chorion and decidua 2.
- It is used to predict the risk of preterm birth in pregnant women, with levels greater than or equal to 50 ng/mL at or after 22 weeks indicating an increased risk 2.
Indications for Fetal Fibronectin Testing
- FFN testing is indicated for pregnant women between 22 and 34 weeks of gestation who are at risk of preterm birth 2.
- It can help identify women who are at significant risk of preterm birth and guide management decisions 2.
- A negative FFN result has a high negative predictive value for delivery within 7 days, making it a useful tool for ruling out preterm labor in women with symptoms 3, 4, 5, 6.
Interpretation of Fetal Fibronectin Results
- A positive FFN result is associated with an increased risk of preterm birth, while a negative result indicates a low risk of preterm birth within 7-14 days 4, 6.
- The presence of FFN in vaginal secretions is a strong predictor of preterm birth, with a relative risk of 25.9 for delivery within 7 days 4.
- The absence of FFN in vaginal secretions has a high negative predictive value, making it a useful tool for avoiding unnecessary interventions in women with symptoms of preterm labor 3, 5.