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 completed weeks of pregnancy. The test may help your provider predict your chances of having premature birth. Premature birth is birth that happens before 37 completed 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

Most common questions

Am I at risk for preterm labor?

No one knows for sure what causes a woman to have preterm labor. But if you have certain risk factors, you're more likely than a woman without risk factors to have preterm labor. Risk factors include: having already had a premature baby or getting pregnant again too soon after having a baby; being pregnant with twins or more; and having problems with your uterus or cervix. You're more likely to have preterm labor if you're underweight or overweight or if you have health problems, like high blood pressure, diabetes or certain infections. Things in your life like stress, smoking, drinking alcohol and using drugs also put you at risk. Talk to your provider if you have any of these risk factors. You may be able to reduce your risk and have a better chance for a healthy pregnancy.

How do I know I’m in labor?

You'll know you're in labor if:

  • You have strong and regular contractions that last 30 to 60 seconds and come 5 to 10 minutes apart.
  • Your water breaks. Your baby has been growing in amniotic fluid (bag of waters) in your uterus. When the bag of waters breaks you may feel a big rush of waters or you may feel just a trickle.
  • You bleed a little from your vagina. This is called bloody show.

If you think you're in labor, call your health care provider, no matter what time of day or night.

How early can a baby be born and live?

There is no set timeline for survival for babies born early. Babies born earlier than 23 weeks have a much smaller chance of survival than babies born after 23 weeks.

About 9 out of 10 babies born at 28 weeks survive. But many have serious health problems. Any baby born before 37 completed weeks of pregnancy is considered premature. Premature babies have less time to develop in the womb than babies who arrive on time. This puts them at greater risk of medical and developmental problems. Every extra day in the womb helps the baby develop and mature and probably improve his or her health and development later in life. Between 23 and 26 weeks, every extra day in the womb increases a baby's chance of survival by 2 to 4 percent.

©2013 March of Dimes Foundation. The March of Dimes is a non-profit organization recognized as tax-exempt under Internal Revenue Code section 501(c)(3).