What Is the Fetal Fibronectin Test? And How Does It Affect Preterm Labor?

pregnant person at doctor's office

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When you're pregnant and thinking about what labor will be like, you're probably not expecting to go into premature labor. Most pregnancies progress to full term without issue. However, unfortunately, sometimes complications do arise. This is why it's important to watch for signs of preterm labor and get regular prenatal care, which may include certain diagnostic tests to make sure your baby is as healthy as can be.

The fetal fibronectin (fFN) test is a diagnostic tool that healthcare providers use to determine the risk for preterm labor. The test measures levels of the protein fetal fibronectin (FFN). Higher levels of the protein, which is measured by collecting fluid in the vagina or cervical opening, indicate whether or not preterm labor is likely. A positive test result means a greater risk of going into labor, while a negative result makes going into labor early less likely.

Here we'll discuss what FFN and the fFN test are in more depth, as well as signs of preterm labor to look out for.

What Is Fetal Fibronectin?

Fetal fibronectin is a protein that is made during pregnancy. "FFN is produced by the cells at the edge of the amniotic sac and the uterus. FFN can be elevated in the vaginal secretions during the first 24 weeks of pregnancy but diminishes between 24 to 34 weeks in normal pregnancies," says Melissa Deer Pelletier, DO, OB/GYN at Northwestern Medicine Central DuPage hospital in Illinois.

Fetal fibronectin protein plays a role in adhering the amniotic sac to the uterus. The protein is present in vaginal secretions in early pregnancy but levels wane in the second trimester. FFN should be low or absent after about the mid-point of gestation. When FFN levels are detectible after around 22 weeks gestation, the risk of going into preterm labor is elevated over the next seven to 14 days.

"FFN in the secretions between 24 to 34 completed weeks is reported to be associated with preterm delivery in symptomatic and asymptomatic pregnant women," explains Dr. Deer Pelletier.

What Is the Fetal Fibronectin Test?

The fetal fibronectin test is a fairly simple, quick, low-discomfort procedure that healthcare providers can do in their exam rooms. The test itself is similar to getting a pap smear and results are typically available within 24 hours.

Some people and pregnancies are at higher risks for preterm delivery. These pregnancies will be more closely monitored by their healthcare providers. However, sometimes preterm delivery can happen even if a person isn’t considered a risk for it. The fetal fibronectin test can help assess the potential for preterm delivery and is typically used after 22 weeks gestation when other signs of impending labor are present.

How Is the Test Done?

Essentially, the goal of the test is to get a sample of vaginal fluid to test for FFN. To begin the test, the patient lies on their back on the exam table. Next, the provider inserts a speculum into the vagina. "A long cotton swab is placed into the vagina near the cervix for 10 seconds, and the swab samples the secretions from the cervix and vagina. This swab is then sent to the lab for evaluation," says Dr. Deer Pelletier.

When Is the Test Done?

This test is typically done in patients beyond 22 weeks who are showing signs of preterm labor. It is not usually done in pregnancies that are asymptomatic unless there are other risk factors, such as previous preterm deliveries, having a short cervix, no or limited prenatal care, previous miscarriages, a history of chronic health conditions, or having other complications with the uterus, cervix, or placenta that increase the risks of early labor.

"The fFN test is FDA approved for use in symptomatic patients between 24 and 34.6 weeks and for asymptomatic patients between 22 and 30.6 weeks. This aids in assessing the risk of preterm delivery in seven or 14 days from the time of vaginal swab collection in pregnant women with signs/symptoms of early preterm labor, intact membranes, and minimal cervical dilation (less than 3 centimeters) sampled between 24 and 34.6 weeks," says Dr. Deer Pelletier.

The test is not typically done after 35 weeks because FFN levels tend to rise after that point, so interpreting results would be less conclusive.

What Does a Positive Test Mean?

A positive test result means that the FFN protein showed up in the vaginal secretions. This finding increases the likelihood of going into preterm labor within the next seven to 14 days. However, this result just elevates the risk of preterm labor. Each person's risk varies greatly depending on the specific circumstances occurring with the pregnancy, as well as any other pertinent complications or medical issues that may be at play.

Healthcare providers use the test result to inform their treatment approach, says Dr. Deer Pelletier. "This is a helpful guide to delineate the next steps for patients with symptoms of preterm labor, such as contractions or cramps."

Getting a positive test result allows for timely and appropriate interventions, such as steroids for lung maturity and magnesium sulfate for fetal brain protection, and allows hospitals to transfer patients at high risk to hospitals with appropriate a NICU," explains Dr. Deer Pelletier.

Getting a positive test result does not mean that you will go into preterm labor. However, it does put you at greater risk of that happening, says Dr. Deer Pelletier. Most importantly, knowing this information can help you get the best care possible to prevent or delay labor, if possible, and/or get you and your baby the best possible care if you do have a premature delivery.

What Does a Negative Test Mean?

If you get a negative fetal fibronectin test, this means that the protein was not detected in a concerning amount. This is a positive sign, says Dr. Deer Pelletier. "A negative fFN test indicates a less than 1% risk of delivery in the next 14 days." Knowing that FFN is not present can help healthcare providers avoid unnecessary interventions, procedures, and hospitalizations. Additionally, a negative result provides a great degree of comfort that labor is not imminent.

Signs of Preterm Labor

Your OB/GYN will continually evaluate your pregnancy for complications, such as indications of preterm labor, at each prenatal appointment. However, it's also key to know the warning signs and to consult your provider if you notice them or experience anything else that concerns you.

Signs of preterm labor include having contractions, cramping, abdominal pain, pelvic pressure, or cervical dilation. Preterm labor can happen in otherwise healthy pregnancies but are more likely to occur in those that are high-risk. Carrying multiples, being underweight or overweight, smoking, having certain medical conditions, experiencing trauma or extreme stress, and using alcohol or illegal drugs are some factors that make preterm labor more likely.

If you are experiencing any signs of preterm labor, contact your medical care provider right away to get appropriate treatment, says Dr. Deer Pelletier.

A Word From Verywell

The fetal fibronectin test is a diagnostic tool that helps healthcare providers gauge how likely it is that a person will go into labor prematurely. It is often used when signs of preterm labor are present. If the test comes back positive, it means there is a greater chance that preterm labor is imminent. If the test result is negative, it means the risk of going into labor early is quite low.

If you suspect that you are in preterm labor or if you have any other questions or concerns, call your healthcare provider right away. While preterm labor can not always be stopped or prevented, prompt care is the best chance you have for postponing labor.

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5 Sources
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