Fetal Fibronectin (fFN)

Fetal fibronectin (fFN) is a protein made by pregnant people. It helps keep the amniotic sac attached to your uterine lining during pregnancy. A fetal fibronectin test checks a person’s risk of preterm birth by measuring fFN in vaginal fluid.


What is fetal fibronectin (fFN)?

Fetal fibronectin (fFN) is a protein that helps keep the amniotic sac attached to the lining of your uterus during pregnancy. The amniotic sac is the fluid-filled membrane that surrounds the fetus inside your uterus. Fetal fibronectin acts like an adhesive that helps the amniotic sac stick to the wall of your uterus. Fetal fibronectin can leak into your vagina if this connection breaks.

If your pregnancy care provider suspects you’re at risk for premature labor, they may use a fetal fibronectin test to check for fetal fibronectin in your vaginal fluid. There shouldn’t be any fetal fibronectin in your vaginal fluid before 35 weeks of pregnancy. If the result of your fFN is positive, it means your amniotic sac isn’t sticking to your uterus.

A positive fFN means you’re at risk of delivery over the next seven to 14 days.


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When is a fetal fibronectin (fFN) test performed?

In most cases, pregnancy care providers do a fetal fibronectin test only if a person shows signs of preterm labor. These symptoms may include:

  • Uterine contractions.
  • Abdominal pain or cramping.
  • Dull lower backache.
  • Changes in vaginal discharge like a bloody show or losing your mucus plug.
  • Signs of dilation (opening of your cervix).
  • Pelvic pressure or pain.
  • Preterm premature rupture of the membranes or PPROM (your water breaks early).

Providers may also perform fFN tests for people at high risk for premature birth, even without any signs of labor. Factors that increase your risk for preterm birth include:

  • A history of preterm delivery.
  • Certain surgeries on your cervix or uterus.
  • Lifestyle factors, including smoking during pregnancy and low pre-pregnancy weight.
  • A short cervix.
  • A short period of time between pregnancies.

Providers generally don’t recommended this test for low-risk pregnancies or people with no symptoms of premature labor.

In what week of pregnancy is the test performed?

A fetal fibronectin test happens between 22 and 34 weeks of pregnancy. The fetus is less likely to develop severe complications of preterm birth after 35 weeks of pregnancy. For this reason, providers don’t usually test for fFN after 35 weeks.

Test Details

How should I prepare for a fetal fibronectin (fFN) test?

A few factors may make a fetal fibronectin test less accurate. If your healthcare provider recommends an fFN test, you should avoid:

  • Placing products such as lubricants, soaps, suppositories or douches in your vagina.
  • Routine pelvic examinations or transvaginal ultrasounds.
  • Sexual intercourse for 24 hours before the test.
  • Anything else that physically disrupts your vagina, cervix or uterus.

Your provider won’t perform the test if you’ve experienced moderate to heavy vaginal bleeding as this can affect test results.


How does a fetal fibronectin (fFN) test work?

Your healthcare provider inserts a long, thin cotton swab into your vagina. This swab collects a small sample of vaginal fluid from your cervix or from the back of your vagina. A laboratory reviews the sample to check for fFN.

How is a fetal fibronectin test measured?

A fetal fibronectin test can either be positive or negative. If the test is negative, there are no traces of fetal fibronectin in your vaginal fluid. If your result is positive, it means your vaginal fluid contains fetal fibronectin. This tells your provider that you’re at risk for premature birth.

What are the risks of the test?

The test itself is safe. However, there’s a risk of a false-positive result. This is especially the case if you place anything inside your vagina in the 24 hours leading up to your test.


Results and Follow-Up

What do the results of my fetal fibronectin (fFN) mean?

Results of your test will be positive or negative.

A positive result means:

  • There’s fetal fibronectin in your vaginal fluid.
  • You’re at risk for premature labor and delivery within the next one to two weeks.
  • Your pregnancy care provider may take steps to prepare you for an early birth such as giving you steroids to help develop the fetus’s lungs.
  • Your provider may give you medications to stop or slow your contractions.

A positive result doesn’t guarantee an early birth. It simply allows your provider to monitor you more closely and offer any necessary treatment.

A negative result means:

  • There was no fetal fibronectin in your vaginal fluid.
  • You’re not at risk for premature birth in the next one to two weeks.
  • Your provider may test you for fetal fibronectin again in seven to 14 days.

Depending on your symptoms and condition, your pregnancy care provider may order additional tests like an ultrasound.

What happens after a positive fetal fibronectin test?

A positive result doesn’t necessarily mean you’ll go into labor within the next seven to 14 days, however, it does mean you have a greater chance. Your pregnancy care provider begins preparing for early delivery by:

  • Giving you corticosteroids to help mature the fetus’s lungs. This may help them avoid respiratory distress syndrome and other problems after birth.
  • Prescribing tocolytics, which are drugs that help slow or stop contractions in people with symptoms of preterm labor.
  • Giving you antibiotics to prevent infection. This is the case if you’ve tested positive for Group B strep or if your water breaks.

How long after positive fetal fibronectin did you deliver?

There isn’t a set time of when you’ll deliver or if you’ll even deliver early. The test only tells your provider that you’re at risk for preterm delivery, not that you definitely will deliver early.

What causes false-positive fetal fibronectin?

You may get an inaccurate result if you place anything inside your vagina in the 24 hours before your test.

How accurate is a fetal fibronectin test?

A positive test isn’t highly accurate at predicting preterm labor. In fact, many people with positive results achieve a full-term pregnancy. A positive result suggests your provider should monitor you closely.

However, a negative result is very accurate in predicting that labor won’t occur in the next 14 days.

When should I know the results of the test?

Because your provider sends your test to a lab for analysis, it may take 24 to 48 hours to get your results. Talk to your pregnancy care provider before the test so you know when you can expect your results.

A note from Cleveland Clinic

If you have symptoms of preterm labor or are at risk for preterm labor, your provider may suggest a fetal fibronectin (fFN) test. It’s a painless test that checks your vaginal fluid for a specific protein that helps “glue” the amniotic sac to your uterus during pregnancy.

Medically Reviewed

Last reviewed on 12/16/2022.

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