Fetal Fibronectin (fFN)

Also Known As

fFN

This article was last reviewed on

April 17, 2018.

This article waslast modified on November 22, 2019.

At a Glance

Why Get Tested?

To help evaluate a pregnant woman's risk of preterm delivery

When To Get Tested?

When you are 22 to 35 weeks pregnant and are having symptoms of premature labor; sometimes if you are at high risk, such as if you have had a previous preterm delivery or have a short cervix

Sample Required?

A swab is used to take a sample of cervical or vaginal fluid from the posterior portion of the vagina or from the area just outside the opening of the cervix.

Test Preparation Needed?

Anything that physically disturbs the cervix or uterus has the potential to elevate fFN levels. Therefore, your healthcare practitioner should collect the sample before a pelvic examination or vaginal ultrasound. Semen may contain enough fFN to create a positive test result, so sexual intercourse should be avoided within 24 hours of sample collection. Avoid lubricants, lotions, soaps, and douches at least a day before the test.

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The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Fetal fibronectin (fFN) is a protein produced at the boundary between the amniotic sac (which surrounds the baby) and the lining of the mother's uterus (the decidua). Fetal fibronectin is largely confined to this junction and is thought to help "glue" or maintain the integrity of the boundary between the amniotic sac and the lining of the uterus. A fetal fibronectin test detects fFN in vaginal fluid to help predict the short-term risk of premature delivery.

According to the American College of Obstetricians and Gynecologists (ACOG), a normal pregnancy is about 40 weeks, with a woman going into labor between 37 and 42 weeks. A preterm delivery is one that occurs between 20 and 37 weeks of pregnancy.

fFN is found in vaginal fluids early in pregnancy because of the normal growth and establishment of tissues at the junction between the amniotic sac and uterus, with levels falling when this phase is complete. fFN is also found in fluids from the vagina after 36 weeks when it is often released into vaginal fluids as the body gets ready for childbirth.

However, fFN should not be detectible between 22 and 35 weeks of pregnancy. Elevated levels during this period reflect a disturbance at the junction between the amniotic sac and the lining of the uterus. Elevated fFN in vaginal fluids during these weeks of pregnancy has been associated with an increased risk of preterm labor and delivery. Many pregnant women experience symptoms that suggest preterm labor. These may include uterine contractions, changes in vaginal discharge, backaches, abdominal discomfort, pelvic pressure, cramping, and dilation of the cervix. However, not all symptomatic women will actually have a preterm delivery. The majority will go on to deliver at term.

Unfortunately, while premature births can have successful endings, serious complications are possible when a baby leaves the womb early. Premature babies frequently have difficulty breathing and feeding. Their lungs and other organs are immature and do not function normally, and the strain on them can cause persistent health problems. The more premature the newborn, the more likely it is that he or she will experience complications.

If a healthcare practitioner thinks that a woman might deliver early, she will consider treatments designed to delay delivery. These treatments can have unwanted side effects, however, so knowing whether or not a woman is likely to deliver prematurely helps in the decision on the best course of action. The fFN test is a relatively noninvasive tool that can help distinguish between those women who are likely to deliver shortly and those who are not.

Common Questions

How is it used?
Fetal fibronectin (fFN) is used to test pregnant women who are between 22 weeks and 35 weeks of pregnancy and are having symptoms of premature labor. The test helps predict the likelihood of premature delivery within the next 7-14 days.

The fFN test should only be used for pregnant women who:

Have intact amniotic membranes

Have a cervix that has not dilated more than 3 centimeters

Have only slight vaginal bleeding

Do not have a cervix that has been sewn shut during pregnancy to help keep the baby in the uterus, a procedure (cervical cerclage) used when someone has a weak cervix

The fFN test is not recommended for screening asymptomatic, low-risk women.
When is it ordered?
The fFN test may be ordered when a woman is 22 weeks to 35 weeks pregnant and has signs and symptoms of preterm labor. These may include:

Uterine contractions

A change in vaginal discharge

Backache

Abdominal discomfort

Pelvic pressure

Cramping

Dilation of the cervix

The fFN test may be repeated after 2 weeks if the first fFN is negative and labor symptoms persist beyond the next 7 to 14 days. The test may therefore be repeated several times since each test result is valid for the following 7 to 14 days.

Sometimes the test may be ordered when a pregnant woman is at high risk of preterm labor, for example, if she has had a previous preterm delivery or has a short cervix.

The fFN test is not meant to be used for women with placental abruption (premature detachment of the placenta), premature rupture of membranes, placenta previa (a placenta attached to the lower portion of the uterus), or moderate to heavy vaginal bleeding.
What does the test result mean?

A positive fFN result is not very good at predicting whether a woman is experiencing preterm labor and delivery. However, a negative fFN result is highly predictive that preterm delivery will not occur within the next 2 weeks.

In other words, when the fFN test is performed on a pregnant woman who is experiencing signs and symptoms of preterm labor, a negative test result means that there is a less than 1% chance of her having a premature delivery within the next 2 weeks. A healthcare practitioner will also use other tests and clinical expertise to evaluate each individual situation.

Since there are risks associated with treating a woman for premature labor (in anticipation of a premature delivery), a negative fFN can reduce unnecessary hospitalizations and drug therapies.

A positive fetal fibronectin test is less specific. It is associated with an increased risk for preterm delivery and with neonatal complications, but it will not tell a woman's healthcare provider whether or not she will deliver early. A positive test suggests the need to monitor a symptomatic woman more closely.
What are the risk factors for preterm labor and delivery?
There are a number of risk factors, but the greatest risk seems to be to women who:

Have had a previous preterm delivery

Are pregnant with multiples

Have a short cervix

Other risk factors include:

Late or no prenatal care

Having certain chronic conditions, such as high blood pressure or diabetes

Having certain problems with the uterus, cervix, or placenta

Having certain infections during the pregnancy

Being underweight or overweight before pregnancy, or gaining too little or too much weight during pregnancy

Smoking, drinking alcohol, or using illicit drugs

Being the victim of abuse or other stressful events

Having multiple miscarriages

Maternal age (less than 18 or more than 40 years) and race seem also to be factors, with African American women at significantly higher risk than Caucasian or Hispanic women.
Why not use the fFN test after 35 weeks?

Because fFN levels normally rise as full-term delivery nears and because a baby who is born at or near full term is less likely to suffer premature complications, testing this late in pregnancy is not generally recommended.
Can preterm labor and delivery be prevented?

Generally, no but if the risk for preterm delivery is high, extra measures can be taken to delay delivery for as long as possible and to help prepare the baby for birth. Drugs (tocolytic agents) can be used to help inhibit uterine contractions and the hormone progesterone can help to reduce the incidence of preterm birth in women who have a history of preterm births. Corticosteroids can be given to the woman to help mature the baby's lungs and help prevent neonatal respiratory distress syndrome (RDS). In addition, the woman may be put on bedrest or hospitalized and may be transferred to a hospital that has the expertise and equipment to handle premature births.
What other tests are used to help determine the risk of preterm delivery?

Other tests include measurement of cervical length as determined by transvaginal ultrasonography and testing for bacterial vaginosis.
Is there anything else I should know?

Vaginal bleeding can interfere with the fFN test. If a pregnant woman is experiencing vaginal bleeding, the test will probably not be performed.

See More Common Questions See Less Common Questions

View Sources

Sources Used in Current Review

Ross, M. (2017 September 7, Updated). Preterm Labor. Medscape Obstetrics & Gynecology. Available online at https://emedicine.medscape.com/article/260998-overview. Accessed on 2/11/18.

(2016 November). Preterm (Premature) Labor and Birth. American College of Obstetricians and Gynecologists. Available online at https://www.acog.org/Patients/FAQs/Preterm-Premature-Labor-and-Birth. Accessed on 2/11/18.

Ruma, M. et. al. (2017 December). Current perspectives on the use of fetal fibronectin testing in preterm labor diagnosis and management. Am J Manag Care. 2017 Dec;23(19 Suppl):S356-S362. Available online at https://www.ncbi.nlm.nih.gov/pubmed/29297658. Accessed on 2/11/18.

Burd, I. (2016 May 16, Updated). Preterm labor. MedlinePlus Medical Encyclopedia. Available online at https://medlineplus.gov/ency/patientinstructions/000486.htm. Accessed on 2/11/18.

Blackwell, S. et. al. (2017 October 3). Utilization of fetal fibronectin testing and pregnancy outcomes among women with symptoms of preterm labor. Clinicoecon Outcomes Res. 2017 Oct 3;9:585-594. Available online at https://www.ncbi.nlm.nih.gov/pubmed/29042802. Accessed on 2/11/18.

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