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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Preterm Labor and Preterm Premature Rupture of Membranes
Sponsored by The Indian Health Service Clinical Support Center
6. Fetal fibronectin
Fetal fibronectin is, simplistically, the extracellular matrix protein that helps attach the fetal chorion to the maternal decidua . As parturition approaches it is released into the cervix and vagina through proteolysis. Its clinical utility derives from its ability to help you triage your patient. The negative predictive value of fetal fibronectin ( fFN ) is over 95 per cent in almost all published studies involving symptomatic women (those having premature contractions).
So…. if your patient has a negative fFN , you can be reasonably well assured that she will not deliver in the next 7 days, and probably not before 37 weeks. The positive predictive value of fFN is poor however. Most studies show that symptomatic women with a positive fFN have only a 12-15 per cent chance of delivering within the next 7 days, so a positive test is clinically much less useful, but still may be helpful with the patient's triage.
The turnaround time for fFN is usually about two hours, a good interval to watch the patient for cervical change. A caveat with its use is that a false positive can be produced by blood, lubricant, amniotic fluid, or semen in the vagina within the last 24 hours. If these conditions can be ruled out, collect a cervico -vaginal specimen at the time you obtain your sample for ferning , and before you do a digital exam with lubricant. If PTL is a frequent problem at your institution, you should certainly consider adding this test to your laboratory's armamentarium. Unfortunately, fFN is not that helpful to predict preterm delivery in asymptomatic women however. In this situation, a positive fFN has a positive predictive value for delivery at less than 35 weeks of only 4-5 per cent, not worth your screening women who you feel are high-risk by their history.
