Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (931 page)

FIBRONECTIN, FETAL (fFN)

   Definition

   This protein is located at the choriodecidual interface, between fetal membranes and the lining of the uterus. It acts as a kind of “glue” that binds the fetus to the mother. The fFN test measures the protein “leaked” through the cervix into the vagina in pregnancy’s final stages, as the fetus prepares for the birth process.

   
Normal range:
negative.

   Use

   To predict the risk of preterm delivery in symptomatic patients, since identifying women with preterm contractions who will go on to deliver prematurely is an inexact process

   To identify asymptomatic women, usually in a high-risk group (e.g., previous preterm delivery, multiple gestation), who are most likely to deliver preterm

   Interpretation

Increased (Positive) In

   Up to 40% of women with signs and symptoms deliver within the next 7 days.

   A woman tested at 24 weeks is nearly 60 times more likely to deliver within the next 4 weeks compared with a woman with a normal fetal fibronectin test when taken between weeks 22 and 24. The test detects nearly two thirds of the preterm births that occur prior to 28 weeks.

Decreased (Negative) In

   99.5% of women with signs and symptoms will not deliver within the next 7 days.

   Less than 1% of women with identified risk factors will deliver before 28 weeks if they have a normal fetal fibronectin test result at 22–24 weeks.

   Limitations

   fFN results should not be interpreted as absolute evidence for the presence or absence of a process that will result in delivery in <14 days from specimen collection in symptomatic women or delivery in ≤34 weeks, 6 days in asymptomatic women evaluated between 22 weeks, 0 days and 30 weeks, 6 days of gestation.