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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 sometimes done when preterm labor symptoms are present. When the fetal fibronectin test is negative, it is unlikely that you are having preterm labor. But even if the test is positive, it does not mean for sure that you are having preterm labor.

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.