Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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        Fetal Fibronectin Test, Cervico-Vaginal Fluid
      

Some 10% of USA births are pre-term (earlier than 37 weeks), and this group has by far the highest rate of neonatal deaths and complications.  So, great efforts are made to prevent true labor and delivery prior to 37 weeks. [Jan. 2008 test performance memo] Patients are becoming aware of this time frame such that it has begun to be a test we handle from the OB's office.

Having first offered the test through LML in 1995, the LMC laboratory is again (as of 10/8/07) offering testing for fetal fibronectin, in house, 24/7.  Fetal fibronectin is an adhesive glycoprotein "isoform" of fibronectin at the maternal-fetal interface whose presence in vaginal fluid can be used to help predict the short-term risk of premature delivery. Fetal fibronectin is produced at the boundary between the amnionic sac and the lining of the mother’s uterus, presumably as the decidua basalis & parietalis lyse in the central zone of those decidual layers (which can be deficient in "placenta accreta").  It is normally detectable in cervicovaginal fluid during early pregnancy and then again after about 36 weeks. During normal pregnancy it is not detectable between 24 and 36 weeks. Elevated levels during this time are associated with an increased risk of preterm labor and delivery. A negative result in a symptomatic pregnant woman is highly predictive (99% probability) that preterm delivery will not occur within the next 7...possibly 14 days, which can reduce unnecessary hospitalization and tocolytic drug therapies.

BIG INHIBITOR to doing test:Test is performed on a vaginal fluid sample, and that vagina must have been "virginal"...no sex & no vaginal instrumentation & no manual exam (no "OB checks") & nothing that could have disturbed the cervix & no foreign fluids (such as KY jelly, betadine, Monstat, etc.)...for 24 hours prior to sample collection or " false positivity" could happen on that test. Patients come to the hospital thinking they are in labor at odd hours, and someone has usually done a cervix-disturbing "check" by the time the obstetrician assesses the situation. The sample must be obtained before any physical examination, and the only originally acceptable collection kit is that supplied by the lab from Adeza.

Test is referenced to a calibrator and triggers a "positive" result when the test value is higher than the calibrator value & "negative" when lower.

Negative, Non reactive, undetectable status:

  • a TRUE negative test indicates that pains and cramps are not true labor in some 95% of cases; the patient does not need hospital admission or tocolytic (labor-stopping) medications. (Negative test means "negative for labor").
  • BUT, an exception to the rule is if the cervix is equal to, or greater than, 3 cm. dilated...those so dilated will likely deliver within 5 days.
  • If the polyester-tipped swab is not cleanly applied to the undisturbed cervix or posterior fornix , it might "sop up" vaginal fluid which has little or no intra-uterine, trans-cervical, fibronectin containing fluid & give a false negative result.

Causes of Positive/Detectible Levels

  • Only 13% of labor-symptomatic mothers before 37 weeks with a positive test result are actually in labor ("positive" test does NOT mean "positive for labor").
  • about 25% with positive test will deliver within 7 days.
  • semen contamination by intercourse within past 24 hours may give a "positive".

Test Synonyms

Other names for this exact or approximate agent are: Fetal Fibronectin, fFN

References:

  1. Adeza insert, HERE.

(posted about 2002; latest addition 6 December 2010)

 
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