From the Guidelines
Fetal Fibronectin (FFN) testing is not indicated for a patient at 35 weeks of gestation. FFN testing is primarily useful between 24 and 34 weeks of gestation when identifying patients at risk for preterm birth has the greatest clinical utility 1. At 35 weeks, the pregnancy is already considered late preterm, and management decisions would typically not be significantly altered by FFN results. If preterm labor is suspected at 35 weeks, clinical assessment and other parameters such as cervical examination and monitoring of contractions would guide management rather than FFN testing. Some key points to consider include:
- The clinical implications of a positive FFN result have not been evaluated fully because no intervention has been shown to decrease the risk of preterm delivery 1.
- A negative test result appears to be useful in ruling out preterm delivery within two weeks 1.
- The test has limited usefulness in low-risk women, and for high-risk women, specific criteria should be met, including testing no later than 34 weeks, six days of gestation 1. Additionally, a positive FFN at this gestational age has poor predictive value for imminent delivery, while interventions to delay delivery (such as tocolytics or corticosteroids) are generally not indicated beyond 34 weeks. The clinical value of FFN lies in its high negative predictive value earlier in pregnancy, which can help avoid unnecessary interventions in patients who are unlikely to deliver preterm 1.
From the Research
Fetal Fibronectin (FFN) Testing at 35 Weeks of Gestation
- The use of Fetal Fibronectin (FFN) testing for assessing the risk of spontaneous preterm birth (sPTB) is supported by various studies 2, 3, 4.
- FFN testing is typically used in conjunction with transvaginal ultrasound (TVU) cervical length measurement to evaluate the risk of sPTB 2, 5.
- According to the studies, FFN testing is most useful for women with symptoms of preterm labor (PTL) between 22 and 36 weeks of gestation 3, 4.
- For a patient at 35 weeks of gestation, FFN testing may still be relevant, as it can help identify women at risk for preterm birth 3, 4.
- However, the evidence suggests that the performance of the fetal fibronectin test is moderate, and its use as a diagnostic tool may depend on local contingencies and future cost-effectiveness analysis 4.
- Other studies recommend the use of TVU cervical length measurement as the primary diagnostic tool for PTL, with FFN testing used in conjunction with TVU in certain cases 5, 6.
Key Considerations
- The American College of Obstetricians and Gynecologists and other organizations have guidelines for the diagnosis and management of preterm labor, which may include FFN testing 6.
- The decision to use FFN testing at 35 weeks of gestation should be based on individual patient risk factors and clinical judgment 3, 4.
- Further research is needed to fully understand the clinical utility of FFN testing and its role in preventing preterm birth 3, 4.