(646) Fetal fibronectin for prediction of spontaneous labor at term

Objective: Elective induction of labor (IOL) at 39 weeks reduces cesarean delivery; however, many individuals hope to labor spontaneously and be informed participants in IOL decision-making. Fetal fibronectin (fFN) predicts risk of spontaneous preterm delivery. We sought to determine if fFN predicts spontaneous term labor.

Study Design:

Prospective observational multicenter study within one healthcare system. Nulliparous patients without a medical indication for IOL prior to 41 weeks were offered enrollment at their 38-week prenatal visit. After informed consent, a provider collected a fFN and performed a cervical exam. The primary outcome was spontaneous onset of labor. The predictor of interest, quantitative fFN value, was dichotomized to positive (≥50 ng/mL) or negative ( < 50 ng/mL) based on qualitative standards in the US. Secondary outcomes included time from study visit until delivery admission. Logistic and Cox proportional hazards regression were used; adjusted models controlled for gestational age and Bishop score at study visit.

Results: 290 patients consented, of whom 284 were included in the analysis with a mean age of 30.1 years and BMI of 24.9. 59% were White, and 22% delivered by cesarean. 173 (60.9%) went into spontaneous labor and 109 (38.4%) were induced, of which 32 (29.4%) were medically indicated and 67 (61.5%) were elective inductions prior to 41 weeks. Mean quantitative fFN value was 46 ± 109 ng/mL, and mean Bishop score was 3.6 ± 2.2 cm. A positive fFN was associated with an increased odds of spontaneous labor (aOR 2.16, 95% CI 1.04 – 4.86, Table). All patients with a positive fFN who were not induced prior to 40w6d (medically indicated or elective) entered labor spontaneously. A positive fFN was associated with an increased adjusted hazard of spontaneous labor (aHR 1.88, 95% CI 1.27 – 2.78, Figure), which persisted after accounting for potential informative censoring due to non-spontaneous deliveries.

Conclusion: A positive fFN is associated with an increased odds of spontaneous labor after 38 weeks. Our findings may help in counseling patients considering elective IOL after 39 weeks.