When to use fetal fibronectin
Diagnosis/definition: Fetal fibronectin (FFN) is a glycoprotein located between the chorion and decidua that is absent or found only in low levels in cervicovaginal secretions between 22 and 34 weeks.
Risk factors/associations: A high level (>50 ng/mL) of FFN in the cervicovaginal secretions at or after 22 weeks increases the risk of spontaneous preterm birth (PTB).
- Currently there is no evidence from randomized trials to suggest that FFN is of benefit in the management of asymptomatic women with a prior PTB (or for other at risk populations, such as twin gestations).
- FFN screening may be more useful in managing symptomatic women with suspected preterm labor at/or before 34 weeks' gestation (Table 1). For these women, a recent meta-analysis of randomized trials found that knowledge of the FFN result is associated with lower incidence of PTB. This benefit was attributed in particular to one trial in which FFN was used in conjunction with transvaginal ultrasound (TVU) assessment of cervical length (CL). About 50% of women with symptoms of preterm labor will have a TVU CL of 30 mm or more, and these women can be reassured since their risk of PTB within 1 week is less than 2% and FFN does not add helpful information. Women with a short cervix, less than 20 mm, are at significant risk for PTB (47%), and a negative FFN test is not adequately reassuring to alter management. FFN seems to be most helpful for women with a 'borderline' TVU CL of 20 to 29 mm. For women with a short cervix less than 20 mm or an intermediate CL with a positive FFN screen, treatment with betamethasone to enhance fetal maturity should be considered, if not previously administered.
- It seems prudent to perform FFN screening using a speculum for direct visualization during specimen collection.
Last Reaffirmed: Aug 1, 2016