Fibronectin Tests: Predicting Preterm Delivery

Frederick R. Jelovsek, MD

Many women have contractions in the last half of pregnancy. the major concern is preterm labor that will lead to an early delivery and a baby at risk of dying or at least spending many days or weeks in the neonatal intensive care nursery. One of the latest tests is fetal fibronectin in the vaginal pool. It has received poor press because it is not very accurate in predicting which patients will prematurely deliver.

Its advantage appears to be as a negative test, i.e. if the test is negative (<0.05 mg/L), the woman is very unlikely to deliver within the next two weeks. One of the best clinical trials in the U.S. is the recent one by Peaceman AM, et al., Fetal fibronectin as a predictor of preterm birth in patients with symptoms: a multicenter trial. Am J Obstet Gynecol 1997;177(1):13-18. Over 700 patients who were examined at the hospital between 24 weeks' and 34 weeks 6 days' gestation were available for analysis. Fetal fibronectin was detected in specimens from 150 (20%) patients. Compared with patients who had positive results, patients who had negative results for fetal fibronectin were unlikely to be delivered within 7 days (0.5%), within 14 days (0.8%), and before 37 completed weeks (16.5%). The authors felt the high negative predictive value of fetal fibronectin sampling supports less intervention for patients with this result.

Some of the European and Scandanavian studies have not shown quite as high specificity, eg. Goffeng AR et al, Fetal fibronectin and microorganisms in vaginal fluid of women with complicated pregnancies. Acta Obstet Gynecol Scand; 1997 76(6):521-527. However, they have had encouraging results. In this study the specificity of fibronectin was 87%, but the study included patients with premature rupture of the membranes. Along with fetal fibronectin, these authors measured for the presence or absence of normal vaginal lactobacilli. They found that the absence of hydrogen peroxide-producing lactobacilli was predictive for preterm delivery < 34 weeks (sensitivity of 100%, specificity 35%).

If these studies hold true, the best strategy would seem to be to be to check fibronectin and for vaginal lactobacilli (or pH <4.5). If the fetal fibronectin is negative, the woman can be sent home. If the fetal fibronectin is positive, but lactobacillis is also present, she may also be sent home.