Fetal fibronectin and preterm labor

During pregnancy, a uterine infection causes inflammation, which can trigger preterm labor. This inflammation can also stimulate the amnion cells to produce fetal fibronectin, a protein.

Fetal fibronectin testing is occasionally done when preterm labor symptoms are present. The absence of this protein indicates with 99% certainty that preterm labor will not occur in the next week. However, a positive test result for fetal fibronectin does not dependably predict preterm labor.¹

For fetal fibronectin testing, a sample of fluid is collected from the vagina or the opening to the uterus (cervix). First, a speculum is used to spread the walls of the vagina to view the cervix. Next, a sterile swab is used to absorb fluid from the cervix or vagina. The speculum is removed and the swab is sent to the laboratory for testing.

A negative test result is quite accurate and shows that labor has not started. A positive test result may show that labor has started, but false-positive results are common. False-positive results can occur if a woman has recently had:

• A pelvic exam. To reduce the risk of a false-positive result, it is important that a fetal fibronectin test be done before a manual pelvic exam.
• Sexual intercourse.
• Uterine contractions.
• Bleeding from the vagina.

The fetal fibronectin test is:

• Somewhat expensive and may not be available in all medical testing centers.
• Not useful for predicting labor in women at risk for preterm labor.
• Helpful only for women with symptoms of preterm labor.

Citations

1. Norwitz ER, et al. (1999). The control of labor. New England Journal of Medicine, 341(9): 660–666.