Fetal fibronectin (fFN) is a fibronectin protein produced by fetal cells. It is found at the interface of the chorion and the decidua (between the fetal sac and the uterine lining).
It can be thought of as an adhesive or "biological glue" that binds the fetal sac to the uterine lining.
Screening test
Fetal fibronectin "leaks" into the vagina if a preterm delivery is likely to occur and can be measured in a screening test.
When the fFN test is positive, it is an inconclusive result. A positive result can indicate that a woman will go into preterm labor soon, but she may not go into labor for weeks. When the fFN test is negative, the result is a better predictor. A negative result means that there is little possibility of preterm labour within the next 7 to 10 days, and the test can be repeated weekly for women who remain at high risk. A negative fetal fibronectin test gives a more than 95% likelihood of remaining undelivered for the next 2 weeks. A systematic review of the medical literature found that fetal fibronectin is a good predictor of spontaneous preterm birth before cervical dilation. The test may be run on patients between 22 and 34 weeks gestation.
The test is easily performed and is usually painless. A specimen is collected from the patient using a vaginal swab. The swab is placed in a transport tube and sent to a laboratory for testing. Most labs can easily produce a result in less than one hour.
A false positive fetal fibronectin result can occur if the test is performed after digital examination of the cervix or after having had intercourse. It is important that the swab be taken before a digital vaginal exam is performed.