Preterm Labour — Viva

Q1: Definition (2 min)

"Define preterm labour and preterm birth."

• Preterm birth (PTB) = delivery before 37 completed weeks (259 days) of gestation.
• Preterm labour (PTL) = onset of regular painful uterine contractions WITH cervical change (effacement and/or dilatation) before 37 weeks.
• Emphasise: contractions alone without cervical change = threatened (irritable) PTL, not established PTL — managed differently (observe).
• Sub-classify PTB: extremely preterm (under 28w), very preterm (28 to under 32w), moderate–late preterm (32 to under 37w).
• Two phenotypes: spontaneous (PTL or PPROM, about 70 to 80 percent) vs indicated/iatrogenic (delivered for maternal/fetal indication).

Q2: Risk factors & pathophysiology (3 min)

"Name the major risk factors and explain the mechanism."

• Strongest: previous spontaneous PTB (recurrence 20 to 30 percent).
• Others: infection (BV, UTI, STI, intra-amniotic — the biggest reversible driver), multiple pregnancy, short cervix, PPROM, uterine anomaly, prior cervical surgery (cone/LEEP), smoking, low BMI, short interpregnancy interval, IVF, antepartum haemorrhage.
• Four convergent pathways on the common pathway of parturition (contractility + cervical ripening + membrane activation):
  1. Infection/inflammation — ascending microbes → cytokines (IL-1β, IL-6, TNF-α) → COX-2 ↑ prostaglandins + MMPs degrade cervical collagen.
  2. Overdistension (twins, polyhydramnios) — stretch → gap junctions, oxytocin receptors.
  3. Vascular/placental — abnormal spiral artery remodelling → ischaemia, abruption.
  4. Endocrine/programmed — functional progesterone withdrawal (PR-A:PR-B shift), rising fetal cortisol, connexin-43.

Q3: Prediction & diagnosis (3 min)

"How do you predict and diagnose preterm labour?"

• Diagnosis is clinical: contractions + cervical change.
• Two rule-out tests (symptomatic woman, intact membranes):
  • TVUS cervical length — 25 mm or less at 20 to 24 weeks, or under 30 mm when symptomatic, = high risk; 30 mm or more = low risk.
  • Fetal fibronectin (22 to 35 weeks) — negative (under 50 ng/mL) = under 1 percent deliver in 7 to 14 days. PPV only about 40 percent. Sample BEFORE digital VE.
• Combined: both negative → discharge without tocolysis/transfer.
• Assessment: speculum BEFORE digital VE (rule out praevia, sample fFN/swabs, assess PPROM with nitrazine/fern); maternal obs (temperature for chorio), CTG, infection screen.

Q4: Management bundle (4 min)

"Outline the management of established preterm labour."

• Aim: delay birth ~48 h for corticosteroids + transfer (NOT stop indefinitely).
• Exclude contraindications to tocolysis FIRST: chorioamnionitis, fetal compromise, abruption, severe pre-eclampsia, 34 weeks or more — if present, deliver.
• Tocolysis: NIFEDIPINE 20 mg PO then 10 to 20 mg every 6 to 8 h (first-line); atosiban (IV, NICE); indomethacin (under 32w, short course). Max 48 h.
• Antenatal corticosteroids (24 to 34w): betamethasone 12 mg IM x2 (24 h apart) or dexamethasone 6 mg IM x4 (12 h apart).
• Magnesium sulfate neuroprotection (under 32w): 4 g IV load over 30 min then 1 g/h; calcium gluconate at bedside; monitor reflexes, respiratory rate.
• GBS prophylaxis: IV benzylpenicillin 3 g then 1.5 g every 4 h.
• In-utero transfer to NICU-capable unit.
• Drug traps: nifedipine + magnesium = severe hypotension; beta-agonists + steroids + twins = pulmonary oedema; indomethacin over 32w = fetal PDA closure/oligohydramnios; amox-clav in PPROM = NEC.

Q5: PPROM & prevention (3 min)

"How do you manage PPROM, and how would you prevent recurrence?"

• PPROM: erythromycin 250 mg QDS PO for 10 days + corticosteroids + magnesium (if under 32w and in labour); surveillance (observations, CTG, WCC/CRP); deliver at 34 weeks (earlier if infection/compromise). AVOID amox-clav (NEC).
• Prevention: vaginal progesterone (short cervix, singleton — Romero 2018); cervical cerclage (history-indicated at 12 to 14w, or ultrasound-indicated rescue); smoking cessation; treat infection; interpregnancy interval. Universal TVUS cervical length screening supported (Hessami 2024). 17-OHPC (Makena) withdrawn 2023 after PROLONG.