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Fetal Fibronectin (fFN) | Lab Tests

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Fetal fibronectin (fFN) is a protein produced during pregnancy. It is produced by cells at the border of the amniotic sac and the mother’s uterus, attaching the amniotic sac to the uterine lining. The amniotic sac surrounds the developing fetus inside the mother’s uterus.

Doctors use a fetal fibronectin test to check a woman’s risk for preterm delivery. Preterm, or premature, delivery is birth occurring before 37 weeks of pregnancy. A normal pregnancy lasts approximately 37-40 weeks.

Fetal fibronectin should not be detectable in vaginal fluids between the 22nd and 35th weeks of pregnancy. If fFN is positive, a women’s risk of preterm delivery is increased over the next 7-14 days.

Fetal fibronectin fFN protein test

When is a fetal fibronectin (fFN) test performed?

In most cases, doctors do a fetal fibronectin test only if a woman shows signs of preterm labor. These symptoms may include:

  • Abdominal pain
  • Backache and cramping
  • Change in vaginal discharge
  • Dilation (opening) of the cervix, the neck of the uterus
  • Pelvic pressure
  • Uterine contractions (pains)

In some cases, doctors perform fFN tests for women at high-risk for premature birth. These women may have the test even without signs of preterm labor. Factors that increase your risk for preterm delivery include:

  • History of preterm delivery or certain surgeries on your cervix or uterus
  • Lifestyle factors, including smoking during pregnancy and low pre-pregnancy weight
  • Short cervix
  • Short period of time between pregnancies
  • Vaginal bleeding during pregnancy

How should I prepare for a fetal fibronectin (fFN) test?

A few factors may make a fetal fibronectin test less accurate. If your doctor recommends a fFN test, you should avoid:

  • Products such as lubricants, soaps, lotions or douches
  • Routine pelvic examinations or pelvic ultrasounds
  • Sexual intercourse for 24 hours before the test

How is a fetal fibronectin (fFN) test performed?

Your doctor inserts a long, thin cotton swab into your vagina. This swab collects a small sample of vaginal fluid from just outside your cervix or from the back of your vagina. A laboratory reviews the sample to check for fFN.

What do the results of my fetal fibronectin (fFN) mean?

Higher fetal fibronectin levels in vaginal fluids between the 22nd and 35th weeks of pregnancy may show a greater likelihood of preterm labor and delivery.

This test does not guarantee an early birth. But the results allow your doctor to monitor you more closely. They help you receive treatment if necessary.

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