Fetal Fibronectin

Fetal Fibronectin
By Wesley J. Kim M.D., December 7, 2000

Background

Preterm delivery is one of the leading causes of perinatal morbidity and mortality. Concerns for the health and well being of both the mother and infant as well as the economic implications (i.e. hospitalization, use of drug therapy such as tocolytics and corticosteroids, and subsequent medical care following delivery) make the diagnosis and management of preterm delivery one of the most challenging problems in obstetrics. The use of a rapid screening tool may help clinicians to make decisions regarding the care of such patients.

Fetal Fibronectin is a complex adhesive glycoprotein that is a normal constituent of the extracellular matrix at the maternal-fetal interface. It is detectable during the first 22 weeks of pregnancy, where it may reflect normal growth of extravillous trophoblasts and the placenta. It is absent between 22 to 34 weeks gestation, and then is again normally detectable after 34 weeks, during the final stages of pregnancy, related to the onset of the birth process. The detection of fetal fibronectin between 22 to 34 weeks is abnormal and indicative of an event at the maternal-fetal interface, which may be associated with increased risk of spontaneous preterm delivery.

[A review of the recent literature shows] Fetal Fibronectin to be among the most effective predictors of preterm delivery. In clinically symptomatic patients, at less than 34 weeks gestation, an elevated fFN showed 76-98% sensitivity and 83-88% specificity for preterm delivery within 7 days from the sample collection. The negative predictive value of fFN ranged from 98-99.5% while the positive predictive value ranged from 13-40%. This negative predictive value has perhaps even more clinical importance than obtaining a positive result as it identifies patients who likely do not require further treatment or hospitalization. In asymptomatic patients, patients at greater than 34 weeks but less than 37 weeks gestation, or for preterm delivery greater than 7 days from the sample collection, the predictive value of fFN is less accurate.

Clinical studies have also validated the economic benefits of risk prediction strategies employing rapid fFN testing with reductions in unnecessary costs for patient transport, preterm labor admissions, length of hospital stay, and prescription of tocolytic agents and corticosteroids, without adversely impacting morbidity and mortality. HMSA currently offers reimbursement for Fetal Fibronectin for symptomatic patients only.

Methodology

DLS will be employing the Adeza Rapid Tli System, which features a monoclonal antibody based lateral flow solid phase immunosorbent device (dry chemistry cassette format) for the qualitative detection of fetal fibronectin in cervicovaginal specimens collected with the Adeza Biomedical Specimen Collection Kit. A sterile swab is used to collect a sample of cervicovaginal fluid, which is then placed in a buffer tube and sent to the lab for analysis. The specimen is extracted into the buffer, filtered, and then dispensed onto the Rapid fFN Cassette, which is inserted into the analyzer. Following a 20- minute reaction time the analyzer interprets and prints out the result.

The fetal fibronectin rapid assay using the Adeza Tli system has been FDA approved for both symptomatic and asymptomatic patients at risk for premature delivery.

Interpretive Information

Negative: In symptomatic patients, there is a 0.5-2.0% chance of preterm birth within 7 days.
Positive: In symptomatic patients, there is a 13-40% chance of preterm birth within 7 days.

References

  1. Ascarelli MH, Morrison JC. Use of fetal fibronectin in clinical practice. Obstetrical and Gynecological Survey, Supplement, 1997.
  2. Leitich H, Egarter C, Kaider A, Hohlagschwandtner M, Berghammer P, Husslein P. Cervicovaginal fetal fibronectin as a marker for preterm delivery: a meta-analysis. Am J Obstet Gynecol 1999; 180 (5): 1169-76.
  3. Lopez RL, Francis JA, Garite TJ, Dubyak JM. Fetal fibronectin detection as a predictor of preterm birth in actual clinical practice. Am J Obstet Gynecol 2000; 182 (5): 1103-6.
  4. Mozurkewich EL, Naglie G, Krahn MD, Hayashi RH. Predicting preterm birth: a cost-effective analysis. Am J Obstet Gynecol 2000; 182 (6): 1589-98.
Test Code Test Name List Price
5447 Fetal Fibronectin $300.00

Test Site: DLS Central Hematology Dept.
Methodology: Solid Phase Enzyme Immunoassay.

Specimen Requirements: Cervicovaginal specimens obtained by using the Adeza Biomedical Fetal Fibronectin Specimen Collection Kit. Kits may be obtained by calling DLS client services at 589-5101. They will also be available at the DLS laboratory and labor and delivery at QMC.
(Sample should be obtained prior to, or at least 24 hours after, digital cervical examination or vaginal probe ultrasound).

Unacceptable Specimens:

  1. Incorrect swabs or samples not obtained by using the Adeza Biomedical Fetal Fibronectin Specimen Collection Kit.
  2. Specimens obtained within 24 hours of sexual intercourse.
  3. Specimens from patients with suspected or known abruption or placenta previa.
  4. Grossly bloody samples.

Storage and Stability: 3 days with refrigeration at 2-8 degrees C.
Test Schedule: Monday thru Saturday, 7:00 am to 10:00 pm.
Testing Time: Minimum of 60 minutes (allow approximately 30 minutes for transportation)
Reference Range: Negative or Positive.
CPT Code: 82731.