Labour and Delivery
Preterm labour is one of the leading causes of neonatal morbidity and mortality worldwide. For every obstetrician, midwife, and medical student, understanding its mechanisms, causes, diagnosis, and management is key to improving outcomes for both mother and child.
Definition
- Preterm labour is defined as the onset of regular uterine contractions resulting in cervical changes (effacement and dilatation) occurring before 37 completed weeks of gestation.
- Preterm delivery (premature delivery) occurs when the baby is born after 28 weeks but before 37 weeks of gestation.
Note: Viability threshold may vary slightly by country — often ≥24–28 weeks.
Classification by Gestational Age
| Category | Gestational Age |
|---|---|
| Extremely preterm | <28 weeks |
| Very preterm | 28–32 weeks |
| Moderate to late preterm | 32–37 weeks |
Why It Matters
- Preterm infants are at risk of respiratory distress syndrome (RDS), hypothermia, intraventricular hemorrhage, necrotizing enterocolitis, and long-term neurodevelopmental problems.
- The earlier the gestational age, the higher the risk of complications.
Etiology (Causes)
Preterm labour can occur spontaneously or be medically indicated (iatrogenic) due to maternal or fetal reasons.
1. Spontaneous Causes
- Infection and inflammation: chorioamnionitis, bacterial vaginosis, urinary tract infection.
- Multiple pregnancy: overstretching of uterus.
- Polyhydramnios: excessive amniotic fluid increases uterine distension.
- Cervical incompetence: painless cervical dilatation in the second trimester.
- Placental abruption: premature separation of placenta.
- Uterine anomalies or fibroids.
- Maternal stress or malnutrition.
2. Medically Indicated Causes
Preterm delivery may be deliberately induced when continuing the pregnancy endangers the mother or fetus:
- Severe pre-eclampsia or eclampsia.
- Placenta previa or abruption with heavy bleeding.
- Severe fetal growth restriction.
- Uncontrolled diabetes or cardiac disease in the mother.
Pathophysiology
Preterm labour is thought to result from premature activation of the normal labour pathway, triggered by:
- ↑ Prostaglandins and cytokines → stimulate uterine contractions.
- Cervical softening and membrane rupture.
- Infection plays a major role through inflammatory mediators that promote uterine activity.
Clinical Features
- Painful, regular uterine contractions before 37 weeks.
- Low backache, pelvic pressure, or abdominal cramping.
- Vaginal discharge or bleeding.
- Cervical effacement and dilatation on vaginal exam.
- Possible rupture of membranes (watery vaginal leakage).
Diagnosis
1. Clinical Diagnosis
- History: timing and frequency of contractions.
- Examination: palpable uterine contractions, cervical changes on speculum/digital exam.
2. Investigations
- Ultrasound: assess gestational age, fetal well-being, and cervical length (<25 mm = risk).
- Fetal fibronectin test: positive result suggests risk of imminent preterm delivery.
- Urinalysis and high vaginal swab: check for infection.
- CTG (Cardiotocography): monitor fetal condition.
Management of Preterm Labour
Management has two goals:
- Delay delivery (to allow fetal maturation).
- Improve neonatal outcome if delivery is inevitable.
1. Initial Assessment
- Confirm diagnosis (rule out false labour).
- Check vital signs, FHR, uterine activity, and membrane status.
- Admit to hospital for observation.
- If membranes ruptured → avoid frequent vaginal exams (infection risk).
2. Tocolytic Therapy (to stop contractions)
Used to delay delivery for 48 hours — enough time to administer corticosteroids.
| Drug | Mechanism | Dose/Route | Side Effects |
|---|---|---|---|
| Nifedipine | Calcium channel blocker → relaxes uterine muscle | 10–20 mg PO, repeat in 20–30 min if needed, then 10–20 mg 6–8 hrly | Hypotension, flushing, headache |
| Atosiban | Oxytocin antagonist → blocks uterine contractions | IV bolus + infusion | Nausea, headache |
| Indomethacin | NSAID → inhibits prostaglandin synthesis | 50–100 mg PR/PO, then 25–50 mg 6–8 hrly (max 48–72 hr) | Oligohydramnios, premature closure of fetal ductus arteriosus |
Contraindications to tocolysis: severe pre-eclampsia, abruption, chorioamnionitis, fetal distress, severe IUGR, maternal cardiac disease.
3. Corticosteroids
Given to accelerate fetal lung maturity and reduce risk of RDS, IVH, and NEC.
- Betamethasone 12 mg IM × 2 doses, 24 hours apart.
- Dexamethasone 6 mg IM × 4 doses, 12 hours apart.
Effective if delivery can be delayed for at least 24 hours after the first dose.
4. Antibiotics
Given if:
- Group B Streptococcus (GBS) positive or unknown status.
- Premature rupture of membranes (PROM) to prolong latency and prevent infection.
Common regimen: Penicillin G or Ampicillin + Erythromycin.
5. Magnesium Sulfate
Given for neuroprotection to reduce risk of cerebral palsy in infants born <32 weeks.
- Loading dose: 4 g IV over 30 min.
- Maintenance: 1 g/hr infusion until delivery or max 24 hours.
Monitor for toxicity: loss of reflexes, respiratory depression, hypotension.
6. Delivery Planning
- If labour progresses despite tocolysis → prepare for preterm delivery.
- Ensure neonatal intensive care unit (NICU) is ready.
- Consider cesarean section for fetal distress or malpresentation.
- In vertex presentation, vaginal delivery is preferred if no contraindications.
Prevention
- Progesterone supplementation in women with history of preterm birth or short cervix.
- Cervical cerclage for cervical incompetence.
- Treat infections promptly (bacterial vaginosis, UTI).
- Smoking cessation and good nutrition.
Summary (High-Yield Points)
- Preterm labour = regular contractions + cervical changes before 37 weeks.
- Main causes: infection, multiple pregnancy, cervical incompetence.
- Diagnosis: clinical exam, ultrasound, fetal fibronectin.
- Management: tocolytics (nifedipine, atosiban) + corticosteroids (betamethasone) + antibiotics if indicated.
- Magnesium sulfate for neuroprotection before 32 weeks.
- Prevention: progesterone, cervical cerclage, infection treatment.