Does Cervicovaginal Fetal Fibronectin Really Play a Role in the Diagnosis of Preterm Labor?
Abstract & Commentary
By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert
Dr. Hobbins reports no financial relationships related to this field of study.
A study that attracted some attention at the Society for Maternal-Fetal Medicine meeting last year was recently published in the American Journal of Obstetrics and Gynecology. It dealt with the usefulness of fetal fibronectin (fFN) and cervical length (CL) in predicting which patients with preterm contractions (PTC) were truly in preterm labor (PTL).
In a collaborative study involving patients in the United States and Chile, Gomez and colleagues evaluated 215 patients admitted to the hospital with PTC and intact membranes with transvaginal sonograms to assess cervical length and examination of vaginal secretions for fFN. All patients were treated similarly with tocolytics.
Forty-three of these patients (20%) delivered prior to 35 weeks. Both tests performed well using receiver-operator curves in predicting those delivering within 48 hours (7.9%), 7 days (13%), and 2 weeks (9%). For example, if CL was < 1.5 cm, 36.7%, 56.7%, and 56% delivered within 48 hours, 1 week and 2 weeks, respectively. If CL was ≥ 1.5, only 3.2%, 5.9%, and 9.2% delivered within 48 hours, 1 week and 2 weeks, respectively. If the cervix was ≥ 3 cm at the time of admission, the chances of delivering within 2 weeks were < 5%.
When fFN was positive 19%, 34.6%, and 42.3% delivered within 48 hours, 1 week, and 2 weeks and, if negative, < 8% delivered within 2 weeks.
Actually, CL was a somewhat better performer than fFN. However, when fFN was added to CL as an adjunctive test at admission, the predictive ability of the combination was impressive. For example, if both were positive (CL of < 1.5 cm), 75% delivered within 1 week of admission, 75% delivered prior to 32 weeks, and 81.3% delivered before 35 weeks. If both tests were negative (CL of ≥ 3 cm), then 2.2% delivered within 1 week and 0% delivered < 32 weeks (Gomez R, et al. Cervicovaginal fibronectin improves the prediction of preterm delivery based on sonographic cervical length in patients with preterm uterine contractions and intact membranes. Am J Obstet Gynecol. 2005;192:350-359).
It is interesting that most early investigation involving both CL and fFN was focused on the ability of each test, performed between 20 and 24 weeks in at-risk patients, to predict preterm delivery later on.1-5 The concept was to earmark patients who might benefit from preventive therapy (unfortunately, with prophylactic regimens that have yet to materialize).
Frankly, one of the most difficult problems providers encounter today involves patients presenting later in pregnancy with preterm contractions. All of the studies to-date indicate that a majority of these patients are not in PTL and yet are subjected to days of confinement while receiving therapy with uncomfortable side effects and some risk (often at a cost exceeding $1,000 per day). A few studies have addressed the ability of fFN or CL to sort out which patients really are at risk to deliver prematurely, but these studies have largely concentrated on one test or the other. This study, while pitting one test against the other, has now shown us that the 2 tests, when used adjunctively, can give the most powerful information as to which patients really are at greatest risk of preterm birth and, just as importantly, which are not.
The main interpretive drawback of this study is that all patients were tocolyzed. Therefore, we do not know if those with reassuring tests might have had the same favorable outcome without tocolytics, as I suspect is true from data from other studies.
Careful review of the results suggests little extra benefit from fFN in patients with a CL of ≥ 3 cm. Interestingly, only 3.7% of those with long cervices and a positive fFN deliver at < 32 weeks compared with 1.1% when fFN was negative. Therefore, deleting the fFN in those with long cervices would decrease expense with a minimal risk of missing a patient destined to deliver at < 32 weeks.
The greatest drawback today to the use of either test is for providers, despite the reams of data in the literature, to have enough confidence in the negative tests to forego tocolytics and continued hospitalization.
- Gomez R, et al. Ultrasonographic examination of the uterine cervix is better than cervical digital examination as a predictor of the likelihood of premature delivery in patients with preterm labor and intact membranes. Am J Obstet Gynecol. 1994;171:956-964.
- Iams JD, et al. Fetal fibronectin improves the accuracy of diagnosis of preterm labor. Am J Obstet Gynecol. 1995;173:141-145.
- Rizzo G, et al. The value of fetal fibronectin in cervical and vaginal secretions and of ultrasonographic examination of the uterine cervix in predicting premature delivery for patients with preterm labor and intact membranes. Am J Obstet Gynecol. 1996;175:1146-1151.
- Goldenberg RL, et al. The preterm prediction study: fetal fibronectin testing and spontaneous preterm birth. NICHD Maternal Fetal Medicine Units Network. Obstet Gynecol. 1996;87:643-648.
- Lockwood CJ, et al. Fetal fibronectin in cervical and vaginal secretions as a predictor of preterm delivery. N Engl J Med. 1991;325:669-674.