Fetal fibronectin

Fetal fibronectin (called fFN) is a protein that acts like a kind of glue. It helps the amniotic sac attach to the lining of your uterus (womb). The amniotic sac is inside the uterus. Its holds your baby and is filled with amniotic fluid.

Your body makes fFN early in pregnancy (up to 22 weeks) and again at the end of pregnancy (about 1 to 3 weeks before labor starts).

What is the fFN test and why is it done?

If you have signs of preterm labor, your health care provider may want you to have the fFN test. Preterm labor is labor that happens too early, before 37 weeks of pregnancy. The test may help your provider predict your chances of having premature birth. Premature birth is birth that happens before 37 weeks of pregnancy.

The fFN test measures how much fFN is in the fluids of your vagina (birth canal) and cervix. The cervix is the opening to the uterus that sits at the top of the vagina.

How is the fFN test done?

The fFN test is like a Pap smear. Your provider uses a cotton swab to collect a fluid sample from your vagina and cervix. She then sends the samples to a lab for testing. Results are usually ready within 1 day.

Your provider also may do a transvaginal ultrasound along with fFN. This is prenatal test that uses sound waves to show a picture of your baby in the womb. Your provider uses ultrasound to:

  1. Measure the length of your cervix, which often shortens before labor starts
  2. Check your baby’s size, age and position in the womb

What do the test results mean?

If the fFN test shows you don’t have any fFN, you probably won’t have your baby for another 2 weeks. Even if the test shows you do have fFN in your fluid, it doesn’t mean you’re going to have preterm labor or birth.

If you have fFN in your fluid, your provider also may use information from ultrasound or other tests to predict your chances of preterm labor. For example, if you’re between 24 and 34 weeks and have fFN in your fluid, you’re at increased risk for preterm labor. If you have symptoms of preterm labor, your provider may recommend taking it easy, taking medicines to help prevent preterm labor or getting corticosteroids for your baby. Corticosteroids are medicines that help speed up your baby’s lung development.

Last reviewed: October, 2012