Fetal Fibronectin Test for Preterm Labor

I am 23 weeks pregnant and heard of a simple new test that can be done to detect the onset of preterm labor. Since I am beginning to dilate already, can they do this test on me now?


Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

I believe the test you may be referring to is called "fetal fibronectin." This test is done by vaginal swab. And it would not be too late to have this done in your case.

For women with a prior preterm delivery, the probability of recurrent preterm birth varies greatly according to both fetal fibronectin and cervical length results. In a large study published in May 1998, in the Am Journal of Ob/Gyn, fibronectin was the most powerful single predictor of preterm birth in women. However, cervical length also contributed by itself to the likelihood of an increased or decreased risk.

Recurrence risk was highest (64 percent) for women with a positive fibronectin whose cervical length was less than 25 mm, and lowest (7 percent) for women with a negative fibronectin results and a cervical length of less than 35 mm.

For women with a cervical length of less than 35 mm (which is normal), the recurrence risk for preterm birth quadrupled from just 7 percent if the fibronectin test was negative to 28 percent if fibronectin test was positive.

Among women whose cervical length was less than 25 mm, the risk of preterm birth before 35 weeks more than doubled from 25 percent if fibronectin testing was negative to 64 percent if fibronectin testing was positive.

It is important to understand that sexual intercourse may affect the diagnosis of preterm labor with use of fetal fibronectin levels because of the existence of high levels in semen, which could create false-positive results. Any positive fetal fibronectin test results should be repeated 96 hours after the episode of intercourse.

This test is not yet in general clinic use but is used in those at risk of preterm labor, such as women with a positive history, women with cervical change or women with multifetal gestation.

Changes in cervical position, cervical consistency and length and cervical dilatation as well as decreasing fetal station (presenting part moving down) may each, or in combination, put a woman at increased risk for preterm birth.

Early dilatation, although something to monitor, is not always an indication of preterm labor. The external opening to the cervix may open slightly, especially in women who have had previous births. It is important to observe for other changes as well, such as thinning of the cervix (shortening) and whether or not the internal os (opening) is dilating as well.

Preterm labor is different from incompetent cervix. A cervix that suddenly dilates with no uterine contractions is more characteristic of incompetence. Such a condition can be managed through the use of a suture placed through and around the cervix to close it.

One of the biggest risk factors for preterm labor is prior occurrence. If you've had a previous preterm birth, your risk is high that you will have another.

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