Mid Pregnancy · Preterm Risk
Fetal Fibronectin (fFN) Test
Cervical swab at 22-35 weeks that predicts preterm birth. Negative result reassures (~99% won't deliver in 14 days). Positive triggers steroids + admission consideration. Combined with cervical length in QUiPP App. NICE-supported.
Last reviewed 2 June 2026
Fetal fibronectin (fFN) interpreter
Cervicovaginal fFN — preterm birth risk
Test type
Result
Enter the fFN result to interpret.
Educational tool only — not medical advice. Sample collection technique matters: swab BEFORE digital cervical exam or speculum, sterile speculum without lubricant, posterior fornix, ≥ 10 seconds. Sample contamination by semen, lubricant, blood, or recent intercourse can cause false positives. NPV ~99.5 % for delivery within 7 days; PPV varies with prevalence.
What does this mean?
Fetal fibronectin is a “glue” protein at the maternal-fetal interface. It’s normally only detectable in cervico-vaginal secretions during the first half of pregnancy and again near term; finding it between 22 and 35 weeks suggests separation of the membranes and an active process that often precedes preterm birth (Lockwood NEJM 1991). The real clinical power is its negative predictive value: ~99.5 % for delivery within 7 days (NICE NG25). That’s why fFN is the standard rule-out test in threatened preterm labour units — a negative result lets clinicians avoid steroids, magnesium, tocolytics and admission in most patients. Positive fFN is less specific; it’s usually combined with cervical length and history in the QUiPP algorithm for a quantitative risk. Sample collection technique matters: swab BEFORE digital exam, no lubricant, no recent intercourse — contaminants cause false positives.
What is fFN?
Protein at the interface between baby’s membranes and the womb. Normally absent in cervical/vaginal fluid 22-35 weeks. Its presence suggests something is disrupting that interface — an early labour signal.
When is fFN used?
- Symptomatic women — contractions, suspected preterm labour.
- Asymptomatic high-risk women — short cervix, previous preterm, multiple pregnancy.
How the swab is taken
- Speculum examination like a smear.
- Cotton-tipped swab against cervix ~10 seconds.
- Usually painless; some pressure.
- Results 10-15 min (bedside machine) or same-day (lab).
Test invalid if: recent sex (24h); recent vaginal exam (24h); bleeding; ruptured membranes.
Positive vs negative meanings
- Negative: <1% chance of delivering within 14 days. Reassuring.
- Positive: increased risk, depends on quantitative level.
Quantitative (qfFN) thresholds for QUiPP
- <10 ng/mL: very low.
- 10-49: low.
- 50-199: moderate.
- 200-499: high.
- ≥500: very high.
If positive
- Antenatal steroids if 24-34 wk.
- Tocolysis to delay labour 24-48h.
- Hospital admission consideration.
- Specialist (in-utero) transfer if early gestation.
- Magnesium sulphate for neuroprotection if <32 wk.
fFN + cervical length together
Combined in QUiPP App with maternal history → percentage risk of delivery within 14/30 days, before 30/34/37 weeks.
Different scenarios
Scenario 1: 28 weeks, contractions, fFN negative
Reassuring. Likely false labour. Home with safety-netting; return if worsening.
Scenario 2: 30 weeks, contractions, fFN 350
High risk. Steroids. Tocolysis 48h. Admit. Specialist transfer if appropriate.
Scenario 3: Previous preterm at 28 wk, this pregnancy 24 wk asymptomatic
Routine fFN + cervical length surveillance. Continues with progesterone.
Scenario 4: 32 weeks, bleeding, fFN attempted
Bleeding invalidates fFN. Cervical length scan + clinical assessment instead.
Scenario 5: Cerclage in place, 28 weeks, contractions
fFN safe with cerclage. Helps decide if delivery imminent + cerclage removal.
Care guidance — fFN
- No vaginal sex 24h before.
- No vaginal exam 24h before.
- Speculum sample; safe.
- Negative reassuring (<1% deliver in 14 days).
- Combine with cervical length (QUiPP).
- Positive triggers steroid + admission consideration.
- Optional — informed choice.
Sources
- NICE NG25. Preterm labour and birth.
- QUiPP App. quipp.org / NICE-supported preterm risk tool.
- Honest C, et al. Fetal fibronectin in predicting preterm birth: systematic review. BMJ 2002.
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Frequently asked questions
What is fetal fibronectin (fFN)?
Protein found at the interface between baby's membranes and the womb. NORMALLY in vaginal/cervical fluid before 22 weeks and after 36 weeks. ABSENT 22-35 weeks unless something is disrupting that interface (early labour signal). PRESENCE in vaginal swab at 22-35 weeks = increased PRETERM BIRTH RISK. SWAB TEST from cervical opening; takes minutes; results often same-day. WIDELY used in UK NHS and US for triage of women with possible preterm labour.
When is fFN used?
TWO main scenarios: (1) SYMPTOMATIC women — contractions, suspected preterm labour, want to know if delivery imminent. NEGATIVE result reassures (high NPV ~99% — unlikely to deliver next 14 days). POSITIVE: increases monitoring + treatment. (2) ASYMPTOMATIC high-risk women — short cervix, previous preterm, multiple pregnancy. ROUTINE swab at 22-35 weeks can help risk-stratify. QUIPP APP combines fFN + cervical length + history for individualised risk.
How is the swab taken?
SPECULUM EXAMINATION — like smear. Cotton-tipped swab placed against cervix for ~10 seconds. NO PAIN usually; some pressure. SAMPLE sent to lab (or bedside test machine — 10-15 min results). REQUIREMENTS for valid test: NO recent vaginal sex (within 24h); NO recent vaginal exam (within 24h); NO bleeding; NO recent vaginal medication; INTACT membranes (waters not broken).
What does a positive fFN mean?
Increased preterm birth risk — NOT guaranteed delivery. Higher the quantitative value (qfFN), higher the risk. CUT-OFFS for QUIPP APP: <10 ng/mL very low risk; 10-49 low; 50-199 moderate; 200-499 high; ≥500 very high. CLINICAL ACTION: monitor + consider antenatal steroids + tocolysis + transfer to specialist unit if labour appears imminent. NOT 'you'll definitely deliver early' — risk gradient.
What does a negative fFN mean?
REASSURING — high negative predictive value. <1% chance of delivering within 14 days if fFN negative + cervix favourable. AVOIDS unnecessary hospital admission, antenatal steroids, NICU transfers. CAN BE DISCHARGED home with safety-netting if otherwise well. POWER of fFN is in its negative predictive value — rules OUT preterm labour reliably.
What if my fFN comes back equivocal / borderline?
RARELY happens with newer quantitative tests. EQUIVOCAL: repeat swab; combine with cervical length scan + clinical assessment; QUIPP APP gives quantitative risk. MOST clinicians use thresholds (e.g. ≥50 ng/mL) but absolute value matters more than 'pos/neg'. MULTIPLE TESTS over time sometimes useful (weekly fFN in high-risk asymptomatic women — protocols vary).
Does fFN replace cervical length scan?
COMPLEMENTARY. CERVICAL LENGTH (TVUS) measures cervix; fFN measures biology. TOGETHER more accurate than either alone. QUIPP APP combines both + history. SHORT CERVIX + POSITIVE fFN = high risk; SHORT CERVIX + negative fFN = lower risk (some can avoid intervention). LONG CERVIX + negative fFN = very reassuring.
Will I need treatment after positive fFN?
DEPENDS on context + level. MODERATE-HIGH risk: ANTENATAL STEROIDS (24-34 wk); TOCOLYSIS to delay labour 24-48h for steroid effect; HOSPITAL admission; specialist (in-utero) transfer to unit with NICU appropriate gestation; MAGNESIUM SULPHATE if delivery imminent <32 weeks. LOW RISK after positive fFN: monitoring; conservative management; aspirin + cervical surveillance. EACH CASE individualised.
Can fFN be done at home?
NO — clinical procedure. SPECULUM examination required for proper sample. NOT a home test like pregnancy tests. ALWAYS done at clinic / hospital. RESULTS from bedside machine or lab. SAFE; takes 5-10 minutes.
What if I'm bleeding?
BLEEDING CONTAMINATES sample — fFN result invalid. NOT useful in: vaginal bleeding; ruptured membranes; recent intercourse (24h); recent vaginal exam (24h); cervical exam disruption. ALTERNATIVE: cervical length ultrasound + clinical assessment. WAIT until bleeding stops if mild and patient stable.
Will fFN harm my baby or pregnancy?
NO. The swab is mild; no impact on baby or pregnancy. SPECULUM exam can occasionally trigger contractions but doesn't cause labour. SAFE in twin / triplet pregnancies. SAFE with cerclage (stitch) in place.
Can I refuse the fFN?
YES — optional. SOME WOMEN prefer cervical length scan alone; some prefer no testing if they wouldn't change management. INFORMED choice. RISKS of refusing: missing useful prognostic information that could trigger steroids / specialist care. DISCUSS with team.
How does QUIPP work?
QUIPP APP combines fFN + cervical length + history (parity, previous preterm birth, current gestation, symptoms) → PERCENTAGE RISK of delivery within 14 days, 30 days, before 30/34/37 weeks. FREE app for clinicians (some integrate into patient discussions). NICE-supported. INFORMS shared decision-making — proceed with intervention or reassure.
What happens if I deliver soon after?
PROTOCOLS in place: STEROIDS (if not given); MAGNESIUM SULPHATE for neuroprotection <32 wk; TRANSFER to specialist NICU if appropriate; NEONATAL TEAM at delivery; resuscitation prep; PARENT counselling (NICU tour if time). MOST preterm babies do well with modern care. EACH WEEK GAINED helps.
How does this relate to other calculators on BumpBites?
Companion: /calculators/cervical-length for ultrasound assessment; /calculators/quipp-app for combined risk; /calculators/vaginal-progesterone-ptb for prevention; /calculators/antenatal-steroids for lung maturation; /calculators/magnesium-sulphate for neuroprotection; /calculators/contraction-timer.