Fetal fibronectin

Screening test

Fetal fibronectin "leaks" into the vagina if a preterm delivery is likely to occur and can be measured in a screening test.

Testing will produce a negative or a positive result. A positive result indicates that fetal fibronectin is present in the cervical secretions. A positive result between 22 and 34 weeks gestation signals an increased risk of preterm birth within the next 7 days. A negative result indicates that there is not fetal fibronectin in the cervical secretions. Fetal fibronectin testing has poor specificity (64%) and positive predictive value (10%). Because of this, the American College of Obstetricians and Gynecologists does not consider positive fFN as diagnostic of prelabor rupture of membranes in the absence of other signs and symptoms and cautions that "these test kits should be considered ancillary to standard methods of diagnosis."

While the specificity and positive predictive value are poor, fetal fibronectin testing has excellent sensitivity (100%) and negative predictive value (100%). Therefore, a negative fFN test is a very strong indicator that preterm birth is not likely to occur within the next 7 days. A 2019 Cochrane Review found that while management based on the results of fFN appeared to reduce preterm birth before 37 weeks, the quality of evidence was low.

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.

At or after 22 weeks of gestation, fFN levels greater than or equal to 50 ng/mL are associated with an increased risk of spontaneous preterm birth.

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 cervical examination or more than 24 hours following intercourse or previous examination.

References

References

1. (July 2019). "Fetal fibronectin testing for reducing the risk of preterm birth". The Cochrane Database of Systematic Reviews.
2. "Fetal fibronectin test". Mayo Clinic.
3. (March 2021). "Fibronectin in development and wound healing". Advanced Drug Delivery Reviews.
4. (September 1991). "Fetal fibronectin in cervical and vaginal secretions as a predictor of preterm delivery". The New England Journal of Medicine.
5. (March 2020). "The diagnostic value of fetal fibronectin testing in clinical practice". The Journal of Obstetrics and Gynaecology Research.
6. (March 2020). "Prelabor Rupture of Membranes: ACOG Practice Bulletin Summary, Number 217". Obstetrics and Gynecology.
7. (July 2019). "Fetal fibronectin testing for reducing the risk of preterm birth". The Cochrane Database of Systematic Reviews.
8. (2008). "The utility of fetal fibronectin in the prediction and prevention of spontaneous preterm birth". Reviews in Obstetrics & Gynecology.