## Fetal Fibronectin (fFN) in Preterm Labor ### Clinical Role of fFN Testing **Key Point:** fFN is a glycoprotein found at the maternal–fetal interface. Its presence in cervicovaginal secretions between 16 and 34 weeks gestation indicates disruption of the decidual–chorionic interface and is associated with preterm birth. ### Test Characteristics | Parameter | Value | |-----------|-------| | Sensitivity | 80–90% | | Specificity | 70–80% | | **Negative Predictive Value (NPV)** | **95–99%** (most useful) | | Positive Predictive Value (PPV) | 20–40% | | Optimal gestational age | 16–34 weeks | | Cutoff for positivity | ≥0.05 μg/mL | ### Clinical Application **High-Yield:** fFN is **most useful as a NEGATIVE test** in symptomatic women. A negative fFN (NPV 95–99%) reliably excludes preterm birth within 7–14 days, allowing safe discharge and reduction of unnecessary interventions. ### Recommended Use 1. **Symptomatic women** (vaginal bleeding, contractions, pelvic pressure) at 16–34 weeks 2. **NOT** for routine screening in asymptomatic women 3. **NOT** for confirmation of diagnosis (low PPV) 4. **NOT** for assessment of fetal lung maturity (use lecithin/sphingomyelin ratio or phosphatidylglycerol) ### Clinical Pearl **Warning:** A positive fFN does NOT mandate preterm delivery; it indicates increased risk. Management depends on gestational age, symptoms, and other risk factors. Approximately 50% of women with a positive fFN will deliver at term. ### Mnemonic **fFN = "Fibronectin's Negative is Nifty"** — A negative result reliably rules out preterm delivery in the next 1–2 weeks.
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