Mayo Clinic Health Library

Fetal fibronectin test

Updated: 05-10-2013

Definition

Fetal fibronectin is a protein that acts as a "glue" during pregnancy, attaching the amniotic sac — the fluid-filled membrane that cushions your baby in the uterus — to the lining of the uterus.

Fetal fibronectin is often present in vaginal discharge before week 22 of pregnancy. Fetal fibronectin also begins to break down and can be detected in vaginal discharge toward the end of pregnancy.

If your health care provider is concerned about preterm labor, he or she might test a swab of secretions near your cervix for the presence of fetal fibronectin between week 22 and week 34 of pregnancy. A positive fetal fibronectin test is a clue that the "glue" has been disturbed and you're at increased risk of preterm labor.

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Why it's done

The fetal fibronectin test is used to rule out preterm labor. It's generally not useful for women who are at low risk of preterm labor, but it can provide valuable information for women who have signs or symptoms of preterm labor or those who are at high risk of preterm labor.

If the fetal fibronectin test is positive, your health care provider will take steps to address premature birth — such as prescribing medication to enhance the baby's lung maturity. If the fetal fibronectin test is negative, you can be assured that your pregnancy is likely to continue for at least another week.

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Risks

The fetal fibronectin test is a simple procedure. The test poses no risk of miscarriage or other pregnancy complications.

However, false-positive results are common, which might cause unnecessary anxiety or treatments.

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How you prepare

You don't need to do anything special to prepare for the fetal fibronectin test.

To avoid a false-positive result, the test will be done before any pelvic exam or vaginal ultrasound. It's also best to avoid having sex for 24 hours before the test.

Vaginal bleeding can affect the test results. If you experience vaginal bleeding, the fetal fibronectin test will likely be postponed.

If the amniotic sac ruptures — your water breaks — the test will be canceled. The amniotic sac is a fluid-filled membrane that cushions your baby in the uterus. If the sac is no longer intact, labor and delivery are inevitable — even if your baby isn't full term.

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What you can expect

During the fetal fibronectin test, you'll lie on your back on an exam table. Your health care provider will place a speculum in your vagina and use a cotton swab to gently swipe secretions near the cervix. The sample will be sent to a lab for analysis. Results are typically available within less than 24 hours.

In some cases, a vaginal ultrasound is done after the sample is taken. During the ultrasound, you'll lie on your back. Your health care provider or technician will place a slender, wand-like device in your vagina to send out sound waves and gather the reflections. The reflected sound waves will be digitally converted into images on a monitor. Your health care provider or technician will use these images to measure the length of your cervix, which often decreases before labor begins. The ultrasound can also help your health care provider or technician assess your baby's size, age and position.

The ultrasound might take up to an hour. It doesn't hurt, and you can return to your usual activities immediately — although your health care provider might recommend other treatments if preterm labor is a concern.

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Results

Results of the fetal fibronectin test are either positive or negative:

  • Positive. A positive result means that fetal fibronectin is present. If you have a positive result between weeks 22 and 34, you're at increased risk of preterm labor. Your health care provider might suggest that you avoid tiring tasks or prescribe a brief course of medication to help prevent preterm labor. You might also be given an injection of potent steroids to speed your baby's lung maturity.
  • Negative. A negative result means that fetal fibronectin isn't present. This indicates that your pregnancy is likely to continue for at least another week. In fact, a negative result might be the most powerful benefit of the test — allowing you and your health care provider to relax a bit with the knowledge that a premature birth isn't imminent.

Whether your test results are positive or negative, remember that prompt recognition of preterm labor might give your health care provider a chance to delay preterm labor or improve your baby's readiness for birth.

If you're concerned that you might be going into labor early, contact your health care provider. Don't worry about mistaking false labor for the real thing.

Warning signs of preterm labor include:

  • Regular or frequent contractions — a tightening sensation in the abdomen
  • Constant low, dull backache
  • A sensation of pelvic or lower abdominal pressure
  • Mild abdominal cramps
  • Diarrhea
  • Vaginal spotting or bleeding
  • Watery vaginal discharge (water breaking) — in a gush or a trickle
  • A change in vaginal discharge
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