What is fetal fibronectin (fFN)?

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.

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

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