Preterm Labour - Overview

• Regular painful/painless uterine contractions
• Cervical dilation ≥3 cm or effacement ≥80%
• Adjunctive tests: transvaginal ultrasound (TVU) cervical length < 30 mm or positive fetal fibronectin (fFN) in cervicovaginal fluid before 34 weeks

Overdiagnosis occurs in 40-70% of suspected cases; fFN and TVU reduce false positives - Creasy & Resnik's MFM, p.897

Tocolysis - Goals and Limitations

1. Administer antenatal corticosteroids (betamethasone/dexamethasone) for fetal lung maturation
2. Transfer the mother to a tertiary care center (in-utero transfer)
3. Possibly allow MgSO₄ neuroprotection to be administered

Tocolytic agents delay delivery in approximately 80% of women, but neither prevent premature birth nor improve adverse fetal outcomes such as RDS. - Goodman & Gilman, p.1904

Tocolytic Agents

The Cochrane analyses concluded that MgSO₄ and oxytocin receptor antagonists are ineffective as tocolytic agents. - Creasy & Resnik's MFM, p.901

Contraindications to Tocolysis

• Severe preeclampsia/gestational hypertension
• Antepartum haemorrhage / abruption
• Chorioamnionitis (infection)
• Significant maternal cardiac disease

• Gestational age >37 weeks
• Fetal demise or lethal anomaly
• Evidence of fetal compromise requiring prompt delivery

MgSO₄ in Preterm Labour - Its Actual Role: Fetal Neuroprotection

Mechanism

• Vascular tone in the fetal brain
• Reduces reperfusion injury
• Reduces cytokine-mediated neurological injury

Evidence

• Multiple observational studies and RCTs show maternal MgSO₄ administration reduces the risk of cerebral palsy (CP) in survivors born preterm
• The NICHD MFMU Network RCT (Rouse et al., n=2241): demonstrated a significant reduction in the rate of moderate or severe CP
• The PREMAG trial (Marret et al.): MgSO₄ before 33 weeks showed significant reduction in late death or gross motor dysfunction at 2 years of age
• The ACTOMgSO₄ trial (Crowther et al., n=1062): lower incidence of CP (6.8% vs. 8.2%), though not statistically significant, with no serious harm
• ACOG/SMFM joint statement (2010): recommends MgSO₄ for fetal neuroprotection in women at risk for imminent preterm delivery at <32 weeks

"ACOG Committee on Obstetric Practice and SMFM issued a joint statement in 2010 recommending the use of magnesium sulfate for fetal neuroprotection before 32 weeks." - Creasy & Resnik's MFM, p.1800

Dosing (Neuroprotection Protocol)

• Loading dose: 4 g IV over 20-30 minutes
• Maintenance dose: 1 g/hour IV
• Treatment continued until delivery or for up to 24 hours
• Gestational age cutoff typically <32 weeks (some protocols use <34 weeks)

MgSO₄ Toxicity and Monitoring

• Patellar (knee-jerk) reflexes - must be present
• Respiratory rate ≥12 breaths/min
• Urine output ≥25-30 mL/hour
• Serum Mg levels if clinically indicated

Other Key Management Steps in Preterm Labour

1. Antenatal Corticosteroids (ACS)

• Betamethasone 12 mg IM x 2 doses 24 hours apart, OR Dexamethasone 6 mg IM x 4 doses 12 hours apart
• Reduces incidence of RDS, IVH (intraventricular haemorrhage), PVL, and neonatal mortality
• Indicated at 24-34 weeks; may be considered 34-36+6 weeks (late preterm)
• A single rescue course may be given if ≥14 days have elapsed and delivery is still imminent

2. GBS Prophylaxis

• If GBS status unknown or positive: Penicillin G IV (or ampicillin)
• Reduces risk of early-onset neonatal GBS sepsis

3. Regionalized Care / Transfer

• Transfer to Level III/IV NICU center if <32 weeks (in-utero transfer preferred)

4. Adjunctive Interventions

• Progesterone (17-OHPC or vaginal progesterone): for prevention in high-risk women (prior spontaneous preterm birth or short cervix), not for acute treatment
• Cervical cerclage: for cervical incompetence, not for active preterm labour

Summary Table: MgSO₄ in Preterm Labour

PROM - Premature Rupture of Membranes (NEET PG OBG)

1. Definitions (MOST important for MCQs)

PROM complicates approximately 8% of all pregnancies - Tintinalli's Emergency Medicine, p.676

2. Aetiology / Risk Factors

• Lower genital tract infections - Chlamydia, gonorrhoea, BV, Trichomonas (most common preventable cause)
• Previous PPROM (strongest predictor of recurrence)
• Cervical incompetence / short cervix
• Uterine overdistension (polyhydramnios, multiple gestation)
• Smoking (increases risk 2-4x)
• Antepartum haemorrhage
• Invasive procedures (amniocentesis, cerclage)
• Nutritional deficiencies (Vitamin C, copper - weakens collagen)
• Low socioeconomic status
• Idiopathic (most cases at term)

3. Diagnosis

A. Clinical Assessment

• Sudden gush of fluid followed by continuous leakage (most classic)
• Fluid is typically colourless, odourless
• Ask about contraction onset (to differentiate from labour)

• Pooling of amniotic fluid in posterior fornix
• Ferning (crystallisation) on microscopy - amniotic fluid forms fern-like pattern when dried on a slide
• Nitrazine (pH) test - amniotic fluid is alkaline (pH 7.1-7.3), turns nitrazine paper blue (normal vaginal pH is acidic 4.5-6.0)
• Valsalva maneuver / fundal pressure - provokes leakage of fluid through cervical os

B. Investigations

PAMG-1 (AmniSure) is significantly more sensitive than nitrazine test (99% vs 88%) - Tietz Textbook of Laboratory Medicine, p.757

C. Amniocentesis

• Indigo carmine dye injection into amniotic cavity - blue dye appears in vaginal pad (definitive but invasive)
• Also used to detect subclinical chorioamnionitis (amniocentesis + culture)

4. Complications

Maternal

• Chorioamnionitis (clinical infection of membranes + liquor - most serious complication)
• Sepsis, endometritis
• Retained placenta, PPH
• Increased C-section rate

Fetal/Neonatal

• Cord prolapse (especially with malpresentation or high presenting part)
• Prematurity (most common cause of neonatal mortality with PPROM)
• Respiratory distress syndrome (RDS)
• Intraventricular haemorrhage (IVH)
• Pulmonary hypoplasia (with prolonged PPROM <26 weeks - oligohydramnios reduces lung fluid, impairs development)
• Skeletal deformities (Potter sequence with previable PROM)
• Neonatal sepsis
• Necrotising enterocolitis (NEC)

5. Management - The High-Yield Section

A. Term PROM (≥37 weeks)

• Most women (90%) will labour spontaneously within 24 hours
• Historically, expectant management was practised, but studies showed immediate induction is preferred - equal or lower infection rates, NO increase in C-section rate
• Induction with oxytocin (or prostaglandins if cervix is unfavourable)
• GBS prophylaxis if positive or unknown status
• Monitor for chorioamnionitis (maternal fever, uterine tenderness, foul-smelling discharge, fetal tachycardia)

Later studies clearly confirmed that immediate induction after term PROM is preferred and does NOT increase C-section rate - Creasy & Resnik's MFM, p.1824

B. PPROM at 34-36+6 weeks (Late Preterm)

• Delivery is generally recommended (benefits of delivery outweigh risks of prematurity at this age)
• Corticosteroids (betamethasone) if not previously given and delivery is not imminent
• GBS prophylaxis
• Antibiotic prophylaxis (latency antibiotics)

C. PPROM at 32-33+6 weeks

• Expectant management with close monitoring
• Antenatal corticosteroids - betamethasone 12 mg IM x2 doses, 24 hours apart
• Latency antibiotics (see below)
• GBS prophylaxis
• Deliver if: chorioamnionitis, fetal distress, labour onset, placental abruption, cord prolapse

D. PPROM at 24-31+6 weeks

• Expectant (conservative) management - main strategy
• Hospitalisation (in a facility with NICU)
• Antenatal corticosteroids (betamethasone)
• MgSO₄ neuroprotection if <32 weeks (4g IV loading dose + 1g/hour maintenance) - reduces risk of cerebral palsy
• Latency antibiotics
• Monitoring for chorioamnionitis, fetal distress
• Do NOT use tocolytics routinely (tocolytic therapy controversial in PPROM - relatively contraindicated)
• Cervical cerclage removal is generally recommended (retention associated with increased neonatal mortality and sepsis)

E. Previable PROM (<22-23 weeks)

• Counsel patient about very poor prognosis
• Options: expectant management vs. termination
• Risk of pulmonary hypoplasia is very high
• If expectant management chosen: same principles as above

6. Latency Antibiotics (NEET PG Favourite)

• Ampicillin 2g IV q6h + Erythromycin 250mg IV q6h for 48 hours, THEN
• Amoxicillin 250mg PO q8h + Erythromycin 333mg PO q8h for 5 days

This is a classic NEET MCQ: "Which antibiotic is avoided in PPROM because it increases NEC risk?" - Answer: Amoxicillin-clavulanate

7. Chorioamnionitis - Diagnosis

• Maternal fever >38°C (most sensitive sign)
• Fetal tachycardia >160 bpm
• Uterine tenderness
• Foul-smelling/purulent amniotic fluid
• Maternal tachycardia >100 bpm
• Elevated WBC count (>15,000)

8. Quick Summary Table (Exam Cheatsheet)

9. NEET PG High-Yield MCQ Points

1. PROM = rupture before labour (not before 37 weeks - that's PPROM)
2. Do NOT do digital examination in PROM - use speculum only
3. Nitrazine test turns blue in amniotic fluid (alkaline)
4. Ferning - amniotic fluid ferns due to NaCl (cervical mucus also ferns - false positive)
5. PAMG-1 (AmniSure) - most accurate bedside test (99% sensitivity)
6. Prolonged PROM >18 hours = increased GBS infection risk
7. Amoxicillin-clavulanate is avoided (causes NEC)
8. Pulmonary hypoplasia = complication of prolonged PPROM <22-24 weeks
9. MgSO₄ is given in PPROM <32 weeks for neuroprotection (not tocolysis)
10. Chorioamnionitis = always deliver, regardless of gestational age
11. Cord prolapse - emergency complication requiring immediate C-section
12. Term PROM + immediate induction = no increase in C-section rate (classic exam point)
13. Latency period is inversely related to gestational age (shorter at term, longer at very preterm)