Fetal Fibronectin (fFN): A Test for Premature Delivery

The fetal fibronectin (fFN) test measures the levels of fFN in secretions from a pregnant woman’s vagina and cervix. According to the American College of Obstetricians and Gynecologists (ACOG), the fFN test may be useful for some pregnant women with symptoms of preterm labor (labor before 37 completed weeks of pregnancy) to help predict their risk of premature delivery (1).

What is fetal fibronectin?
fFN is a protein produced during pregnancy. It acts as a biological glue, attaching the fetal sac to the uterine lining. fFN normally is present in cervico-vaginal secretions up to 22 weeks of pregnancy and again at the end of the last trimester (1 to 3 weeks before labor). fFN usually cannot be detected between 24 and 34 weeks of pregnancy (5˝ to 8˝ months).

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What is the fFN test?
Health care providers give the fFN test to women between 24 and 34 weeks of pregnancy. The presence of fFN during these weeks, along with symptoms of labor, suggests that the “glue” may be disintegrating ahead of schedule and alerts health care providers to a possibility of premature labor and delivery.

Providers use a cotton swab to collect samples of cervico-vaginal secretions during a speculum examination (similar to a Pap smear). Results usually are available within 24 hours. The result is either positive (fFN is present) or negative (fFN is not present).

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What do fFN test results mean?
Most women with symptoms of preterm labor go on to deliver at term, even without treatment (2). The fFN test can help predict which symptomatic women have a reduced risk of premature labor and delivery. Fewer than 5 percent of women with symptoms of preterm labor who have a negative fFN test result deliver within the next 2 weeks (1). Identifying symptomatic women who have a reduced risk of premature delivery is the most valuable use of this test because these women often can avoid unnecessary medical interventions, such as bedrest, prenatal corticosteroids, hospitalization and labor-suppressing (tocolytic) medications (1,3).

Positive fFN test results in women with symptoms of preterm labor are less reliable. However, positive results allow health care providers and pregnant women to take preventive measures to delay labor as long as possible and to consider labor-suppressing medications.

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What other women, besides those with symptoms of labor, may be offered the fFN test?
Health care providers may offer the fFN test to some women at high risk of premature delivery. These women may include those who have had a previous premature delivery and those with a short cervix. Test results can help health care providers manage the pregnancy.

ACOG currently does not recommend routine fFN testing of low-risk, asymptomatic pregnant women because the test is not helpful in predicting premature delivery in these women (1).

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What other tests can help predict premature delivery?
A vaginal ultrasound to measure the length of the cervix also can help predict premature delivery. This test is sometimes done along with the fFN test.

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References

  1. American College of Obstetricians and Gynecologists (ACOG). Assessment of Risk Factors for Preterm Birth. ACOG Practice Bulletin, number 31, October 2001 (reaffirmed 2008).
  2. Berghella, V., et al. Fetal Fibronectin Testing for Reducing the Risk of Preterm Birth (Review). The Cochrane Library, 2009, Issue 2.
  3. American College of Obstetricians and Gynecologists (ACOG). Management of Preterm Labor. ACOG Practice Bulletin, number 43, May 2003 (reaffirmed 2008).

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August 2009