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.
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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In most cases, pregnancy care providers do a fetal fibronectin test only if a person shows signs of preterm labor. These symptoms may include:
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:
Providers generally don’t recommended this test for low-risk pregnancies or people with no symptoms of premature labor.
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.
A few factors may make a fetal fibronectin test less accurate. If your healthcare provider recommends an fFN test, you should avoid:
Your provider won’t perform the test if you’ve experienced moderate to heavy vaginal bleeding as this can affect test results.
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.
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.
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 of your test will be positive or negative.
A positive result means:
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:
Depending on your symptoms and condition, your pregnancy care provider may order additional tests like an ultrasound.
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:
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.
You may get an inaccurate result if you place anything inside your vagina in the 24 hours before your 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.
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.
Last reviewed by a Cleveland Clinic medical professional on 12/16/2022.
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