Using the Fetal Fibronectin Test for Preterm Labor

Pregnant woman sitting in chair in doctors office waiting room
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When you’re pregnant, doctors and midwives will often talk about helping to ensure that you go “full term.” Pregnancy is considered to be 40 weeks, and "full term" refers to having your baby after 37 weeks.

Preterm labor is defined by the American College of Obstetricians and Gynecologists (ACOG) as contractions and cervical changes that occur before 37 weeks of pregnancy, and preterm birth is a birth that occurs between weeks 20 and 37 of pregnancy.

Preterm labor and birth are cause for concern because the health risks to a baby born during this time are increased, complete fetal development hasn't yet occurred, and infant mortality is also increased. The fetal fibronectin test is a tool that is used to help obstetricians and midwives assess for preterm labor.

What Is Fetal Fibronectin?

Fetal fibronectin is a protein that is thought to help secure the amniotic sac to the uterus. Fetal fibronectin naturally occurs in vaginal discharge for up to week 22 of pregnancy, as well as near the end of pregnancy. If the protein is detected between approximately 22 and 37 weeks, it might be cause for concern.

What Is the Fetal Fibronectin Test?

If your doctor or midwife is concerned about preterm labor between those weeks, she might want to do a fetal fibronectin test. This is a simple test that consists of swabbing cervical secretions and sending the sample to a lab to check for fetal fibronectin.

Although it’s a simple test, it’s not done for everyone because, in those who are at low risk for preterm labor, it’s generally not a helpful test. False positives are pretty common, which can add needless stress to your experience. The test is usually used in women at risk of preterm labor and birth, or women who’ve shown symptoms of preterm labor.

Women might be at risk for preterm labor or delivery if they have a short cervix, if there's a short interval between pregnancies if the woman is carrying multiples, if there is a history of prior preterm birth, and certain lifestyle factors like substance abuse. Talk with your doctor about your history and whether you might be at risk for preterm labor if you're concerned about it.

When the Test Comes Back Positive

If the test comes back positive, this means the protein has been found in your vaginal secretions, and you are at risk of preterm labor. Your provider might want to do a vaginal ultrasound to measure the length of your cervix, since cervical length has been correlated with risk of preterm delivery.

They might also take some precautions for a preterm birth. This might include giving you steroids to help your baby’s lungs mature more quickly, or other medications for the fetus. You might also be given medication to stop any contractions you’re having.

If the test is negative, no fetal fibronectin was found in the secretions. If that is the case, your risk of going into preterm labor is likely less for the two weeks after the test is performed, though not necessarily for the remainder of your pregnancy.

Preparing for the Test

Because false positives do occur, it’s important to take some precautions before the test to minimize your chances of getting a false positive and to help ensure your results are as accurate as possible. You don’t have to prepare, per se, for the test, but there are some things you should avoid:

  • Don’t have sex for 24 hours before the test.
  • If you’re having vaginal bleeding, tell your provider, since this can influence the results.
  • Try to avoid lotions or soaps for at least 24 hours prior to the test, as well as douches.

Warning Signs of Preterm Labor

If you have signs or symptoms of preterm labor, call your doctor immediately, even if you’re not at risk for preterm labor. It’s better to be safe than sorry, and your doctor likely feels the same way. Here are some things to be mindful of:

  • Abdominal cramping
  • Changes in or an increase of vaginal discharge
  • Pelvic or lower abdominal pressure or tightening
  • Persistent dull backache
  • Vaginal bleeding or spotting
  • Watery vaginal discharge or your waters break

While the fetal fibronectin test isn’t perfect, it can be a helpful tool for your healthcare provider. If you have a history of preterm labor or birth or are at risk for preterm labor, talk with your healthcare provider about whether a fetal fibronectin test might be helpful for you at some point.

3 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American College of Obstetricians and Gynecologists. Preterm (premature) Labor and Birth. 2016.

  2. March of Dimes. Fetal Fibronectin (fFN): A Test for Premature Delivery. 2009.

  3. Fuchs F, Lefevre C, Senat MV, Fernandez H. Accuracy of fetal fibronectin for the prediction of preterm birth in symptomatic twin pregnancies: a pilot study. Sci Rep. 2018;8(1):2160. doi:10.1038/s41598-018-20447-5

By Jaime R. Herndon, MS, MPH
Jaime Rochelle Herndon, MS, MPH, MFA, is a former writer for Verywell Family covering fertility, pregnancy, birth, and parenting.