The Role of Fetal Fibronectin
Fetal fibronectin (fFN) is a protein produced during pregnancy and functions as a biological glue, attaching the fetal sac to the uterine lining. During the first trimester and for about half of the second trimester (up to 22 weeks of gestation), fFN is normally present in the cervico-vaginal secretions of pregnant women. In most pregnancies, after 22 weeks, this protein is no longer detected until the end of the last trimester (one to three weeks before labor).
The presence of fFN during weeks 24-34 of a high-risk pregnancy, along with symptoms of labor, suggests that the "glue" may be disintegrating ahead of schedule and alerts doctors to a possibility of preterm delivery.
A number of factors are associated with a high risk of preterm delivery. Leading risk factors include a previous preterm birth, multiple pregnancy, an incompetent cervix (a cervix that dilates too early in the pregnancy), uterine abnormalities and amniotic fluid infection. Additional risk factors include vaginal infections and sexually transmitted diseases, maternal smoking and drug abuse, poor nutrition, extremes of maternal weight, and lack of prenatal care. Stress, genetic predisposition and environmental toxins may also contribute to preterm delivery.
The fFN Test
A cotton swab is used to collect samples of cervico-vaginal secretions during a speculum examination (similar to a Pap smear). The analysis of the collected sample usually takes less than 24 hours to complete. The result is either positive (fFN is present) or negative (fFN is not present). The results are valid for up to two weeks from the date of the test.
Recommendations
The greatest value of the fFN test is the high level of reliability of a negative test result. According to ACOG, “Fetal fibronectin testing may be useful in women with symptoms of preterm labor to identify those with negative values and a reduced risk of preterm birth, thereby avoiding unnecessary intervention” (1)
In women with symptoms of preterm labor, a positive fFN result, while less reliable, allows doctors and patients to take preventive measures to delay labor for as long as possible and to consider labor-suppressing (tocolytic) medications.
If the results of fFN negative screening would affect treatment, testing may also be appropriate for women who are asymptomatic, but at high risk of preterm birth. Screening for these women may be done at 24-34 weeks gestation to assist in clinical management (2). In these cases, a negative test result would help prevent unnecessary medical interventions, such as bedrest, prenatal corticosteroids, cervical cerclage, hospitalization and tocolytics.
ACOG currently does not recommend routine fFN screening of pregnant women, as its use has not been shown to be clinically effective in predicting preterm labor in low-risk, asymptomatic pregnancies.
Text References
(1) American College of Obstetricians and Gynecologists. Assessment of Risk Factors for Preterm Birth. ACOG Practice Bulletin, number 31, October 2001.
(2) Iams, J.D. Prediction and Early Detection of Preterm Labor. Obstetrics and Gynecology, volume101, number 2, pages 402-412, February 2003.
Additional References
American College of Obstetricians and Gynecologists. Management of Preterm Labor. ACOG Practice Bulletin, number 43, May 2003.
Andersen, H.F. Use of Fetal Fibronectin in Women at Risk for Preterm Delivery. Clinical Obstetrics and Gynecology, volume 43, number 4, December 2000, pages 746-758.
Elliott, J. Fetal Fibronectin Testing in the Management of Triplets and Quadruplets. Phoenix Perinatal Associates: 1997.
Leitich, H., et al. Cervicovaginal Fetal Fibronectin as a Marker for Preterm Delivery: A Meta-Analysis. American Journal of Obstetrics and Gynecology, May 1999, volume 180, number 5, pages 1169-1176.
Lu, G.C., et al. Vaginal Fetal Fibronectin Levels and Spontaneous Preterm Birth in Symptomatic Women. Obstetric and Gynecology, February 2001, volume 97, number 2, pages 225-228.
Von Der Pool, B. Preterm Labor: Diagnosis and Treatment. American Family Physician, May 15, 1998, volume 57, number 10, pages 2457-2469.
April 2006
