Obstetric Topic 17. Preterm labor and delivery

I. Definition and Causes

Definition

• Preterm labor: regular uterine contractions + cervical change before GW37, after viability.
• Hungarian/Semmelweis framing: after GW24; many international sources use after 20 weeks.
• Preterm delivery: live birth before GW37.
• Importance: major cause of neonatal morbidity and mortality.

Classification

• Extreme preterm: <28 weeks; extremely low birth weight <1000 g.
• Very preterm: 28-32 weeks.
• Moderate preterm: 32-34 weeks.
• Late preterm: 34-36+6 weeks; low birth weight <2500 g.

Etiology / Risk Factors

• Previous preterm birth: strongest risk factor.
• Infection: chorioamnionitis, UTI/pyelonephritis, STIs, GBS.
• Mechanical stretch: multiple pregnancy, polyhydramnios.
• Cervical/uterine: cervical insufficiency, uterine anomalies, fibroids.
• Placental/fetal: PPROM, abruption, placenta previa, IUGR, fetal anomaly.
• Maternal: smoking, alcohol/drugs, stress, poor nutrition, short interpregnancy interval.
• Iatrogenic: indicated early delivery for maternal/fetal disease.

Pathophysiology

• Infection/cytokines, stress/cortisol, placental ischemia/abruption, uterine stretch → ↑ prostaglandins → cervical ripening + uterine contractions.

II. Diagnosis

Clinical Signs

• Regular painful contractions, menstrual-like cramps, pelvic pressure.
• Low back pain, increased vaginal discharge, spotting or fluid leakage.
• Diagnostic contraction pattern: ≥4 contractions/20 min or ≥8 contractions/60 min.
• Cervical change: dilation ≥2-3 cm and/or effacement/shortening.

Tests

• Speculum exam: exclude rupture of membranes, bleeding, infection; avoid unnecessary digital exam if PPROM possible.
• Transvaginal cervical length: <25 mm before 34 weeks → increased preterm birth risk.
• Fetal fibronectin: useful at 22-34 weeks; negative test makes delivery within 1-2 weeks unlikely.
• Ultrasound: fetal growth, presentation, placenta, amniotic fluid, cervical length.
• Labs/cultures: CBC, urinalysis/culture, GBS culture, STI tests if indicated.

III. Management

Initial Approach

• Assess: gestational age, fetal status, contractions/cervix, membranes, bleeding, infection, maternal disease.
• If ≥34 weeks: often admit/observe and allow delivery if true labor.
• If <34 weeks and stable: delay birth briefly if useful for steroids, magnesium or transfer to neonatal center.

Tocolysis

• Goal: delay labor up to 48 h, not long-term prevention.
• Main indication: gain time for corticosteroids, MgSO4 neuroprotection or transfer.
• Options: nifedipine, indomethacin before 32 weeks, atosiban, terbutaline selected cases.
• Nifedipine: common first-line; avoid severe hypotension.
• Indomethacin: avoid after 32 weeks because ductus arteriosus constriction/oligohydramnios risk.
• Terbutaline/beta-agonists: avoid in significant cardiac disease; more maternal side effects.
• Contraindications: chorioamnionitis, significant abruption/bleeding, fetal distress/demise, severe preeclampsia/eclampsia, major lethal anomaly, advanced labor.

Corticosteroids and Neuroprotection

• Antenatal corticosteroids: betamethasone or dexamethasone → fetal lung maturation/surfactant, ↓ RDS and IVH.
• Indication: risk of delivery within 7 days, routinely 24-33+6 weeks; consider from 23 weeks if neonatal resuscitation planned.
• Late preterm steroids: 34-36+6 weeks may be used if high risk of delivery within 7 days and no previous course, according to protocol.
• Magnesium sulfate: fetal neuroprotection for imminent early preterm birth, commonly <32 weeks.

Antibiotics

• GBS prophylaxis: give in preterm labor if GBS positive/unknown according to protocol.
• PPROM: latency antibiotics, e.g. ampicillin/amoxicillin + erythromycin/azithromycin regimen according to local protocol.
• Chorioamnionitis: broad-spectrum antibiotics + delivery; tocolysis contraindicated.
• No routine broad-spectrum antibiotics for preterm labor with intact membranes and no infection.

IV. Complications and Prevention

Fetal / Neonatal Complications

• Respiratory distress syndrome / neonatal ARDS.
• Intraventricular hemorrhage.
• Necrotizing enterocolitis.
• Retinopathy of prematurity.
• Patent ductus arteriosus.
• Neonatal sepsis, hypothermia, hypoglycemia, anemia of prematurity.

Prevention in High-Risk Patients

• Treat infections and stop smoking/substance use.
• History of preterm birth or short cervix → specialist care.
• Short cervix: vaginal progesterone and/or cerclage depending history, cervical length and gestational age.