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Induction of Labour - Detailed Overview

1. Definition and Background

• Elective - performed for convenience of the patient or provider, or logistical/psychosocial reasons
• Indicated - performed for a medical, obstetric, or fetal complication where delivery is safer than continuing the pregnancy

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2. Indications

Medical/Obstetric Indications

• Pregnancy-induced hypertension / Pre-eclampsia / Eclampsia
• Gestational or pre-existing diabetes mellitus
• Premature rupture of membranes (PROM / PPROM)
• Post-term pregnancy (> 42 weeks) - associated with increased perinatal death, fetal macrosomia, meconium aspiration, dystocia
• Fetal growth restriction (FGR) / Intrauterine growth retardation
• Intrauterine fetal death (IUFD) / Fetal demise
• Chorioamnionitis (intra-amniotic infection)
• Rh isoimmunization / significant alloimmunization
• Oligohydramnios or polyhydramnios
• Non-reassuring antepartum fetal testing
• Maternal chronic renal, cardiac, or pulmonary disease
• Obstetric cholestasis (intrahepatic cholestasis of pregnancy)

Logistical/Psychosocial (Elective) Indications

• Distance from hospital / risk of precipitous delivery
• Rapid prior labours
• Psychological or emotional factors (patient request, partner availability)
• Scheduling for physician/hospital coverage

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3. Contraindications

• Previous classical (vertical) uterine incision
• Prior uterine surgery with entry into the cavity (e.g. myomectomy)
• Active genital herpes infection
• Placenta or vasa praevia
• Umbilical cord prolapse
• Transverse or oblique fetal lie
• Cephalopelvic disproportion (CPD)

• Previous low-transverse caesarean section (increased uterine rupture risk; misoprostol is especially cautioned)
• Grand multiparity
• Non-vertex presentation
• Severe fetal compromise where vaginal delivery is unlikely to succeed

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4. Pre-induction Assessment - The Bishop Score

Interpretation:

• Score ≥ 9: Favourable - likelihood of successful vaginal delivery approaches that of spontaneous labour. Average duration of labour ~4 hours in multiparas.
• Score ≥ 8: When oxytocin is used, success approaches spontaneous labour.
• Score 6-8: Induction can proceed; cervical ripening may help.
• Score < 6: Unfavourable cervix - cervical ripening is recommended before oxytocin.
• Score ≤ 5 in nulliparas: ~50% risk of failed induction.

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5. Cervical Ripening Methods

A. Non-Pharmacological Methods

• The examining finger is inserted through the cervical os and swept circumferentially to detach the membranes from the lower uterine segment
• Stimulates local prostaglandin release
• Requires at least some cervical dilation
• Risks: Rupture of membranes, infection, bleeding, irregular contractions
• Generally safe, especially near post-dates

• A 16-26 Fr Foley catheter is placed through the cervical os and inflated with 30-60 mL of saline
• Applies mechanical pressure to the lower uterine segment, stimulating local prostaglandin release
• Cervical ripening by mechanical dilation
• Compared with intravaginal PGE2: similar C-section rates, less likely to cause uterine hyperstimulation, but lower rate of delivery within 24 hours
• Preferred in women with prior caesarean section (lower uterine rupture risk than prostaglandins)

• Hygroscopic cervical dilators made from dried seaweed (Laminaria digitata or japonica)
• Available in small, medium, large sizes
• Absorb moisture, expand, and progressively dilate the cervix overnight

• Amnihook is used to rupture the membranes when the cervix is already favourable (Bishop ≥ 6, vertex engaged, cervix ≥ 2 cm dilated, partially effaced)
• Triggers prostaglandin release, stimulates contractions
• Keettel's large series: only 3.4% needed additional oxytocin when cervix was favourable
• Cannot be reversed once performed; risk of cord prolapse if head not engaged

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B. Pharmacological Methods

• Cervidil has a retrieval system - can be removed if uterine hyperstimulation occurs (advantage over gel)
• May or may not cause uterine contractions; cervical softening appears independent of contraction number
• Previous caesarean section is NOT an absolute contraindication for dinoprostone
• Oxytocin may then be used if spontaneous labour does not ensue

• Synthetic PGE1 (Cytotec); FDA-approved for gastric ulcers; used off-label for induction
• More potent than dinoprostone; associated with shorter time to delivery and lower C-section rates in meta-analyses
• Protocol:
  • 25 μg vaginally (one-quarter of 100-μg tablet) into vaginal fornix
  • Repeat after 4 hours if minimal change
  • Hold if: ≥2 contractions in 10 minutes, Bishop score ≥ 8, active labour, or non-reassuring FHR
  • Do NOT give oxytocin within 2 hours of last misoprostol dose
  • Maximum duration: 24 hours
  • Oral misoprostol 100 mg every 3-4 hours is also safe and effective
• Caution / Avoid in women with prior caesarean section or uterine surgery - significantly increased uterine rupture risk
• For fetuses < 28 weeks: 200-400 μg vaginally or orally every 4 hours

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• IV infusion only, via infusion pump
• Diluted in lactated Ringer's or normal saline: typically 10-20 units in 1 L (= 10-20 mU/mL)
• Steady-state plasma levels reached ~40 minutes after starting infusion

• Goal: Contractions 2-3 minutes apart, 45-60 second duration, 50-75 mmHg intensity, normal resting tone between contractions
• ~90% of patients respond to ≤ 16 mU/min
• Doses > 20 mU/min have antidiuretic (vasopressin-like) effects - risk of water intoxication and hyponatremia (coma, convulsions, death)
• Continuous EFM and uterine activity monitoring mandatory throughout

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6. Confirming Dates Before Induction

1. Fetal heart tones present for 30 weeks (Doppler) or 20 weeks (fetoscope)
2. 36 weeks since positive β-hCG
3. Crown-rump length at 6-12 weeks confirming GA ≥ 39 weeks
4. Ultrasound at 13-20 weeks confirming GA ≥ 39 weeks
5. Documented fetal lung maturity by amniocentesis (if < 39 weeks)

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7. Complications

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8. Management of Hyperstimulation

1. Assess FHR immediately
2. If FHR non-reassuring:
   • IV fluid bolus 1000 mL
   • Lateral (left) positioning of mother
   • Oxygen 10 L/min via non-rebreather mask
   • Discontinue/reduce oxytocin (or remove Cervidil insert)
   • Consider terbutaline 0.25 mg subcutaneously as tocolytic
3. If FHR remains non-reassuring → prepare for immediate delivery (vaginal or caesarean)

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9. Special Situations

Prior Caesarean Section

• Previous low-transverse incision + uterus < 28 weeks: use misoprostol (200-400 μg dosing)
• Previous low-transverse incision + uterus > 28 weeks: oxytocin + Foley catheter ripening (avoid misoprostol)
• Previous classical incision: repeat caesarean is appropriate (IOL contraindicated)

Post-term Pregnancy (> 42 weeks)

• Risks: increased perinatal death, macrosomia, meconium aspiration, labour dystocia
• Induction reduces these risks
• Cochrane review confirms IOL at/beyond term improves birth outcomes

Optimal Timing

• Risk of cerebral palsy is lowest at delivery at 40 weeks - earlier or later increases risk
• The ARRIVE trial (Grobman et al., 6000+ nulliparas) showed elective induction at 39 weeks vs waiting until 41 weeks had no increase in C-section rate and no adverse outcomes

Fetal Demise

• Complete blood count, type and screen on admission; fibrinogen if demise > 4 weeks (DIC risk)
• < 28 weeks: misoprostol 200-400 μg vaginally/orally every 4 hours

• 28 weeks: misoprostol 25-50 μg or standard oxytocin infusion

• Allow spontaneous placental delivery; avoid cord traction to minimize retained placenta
• Rh-negative mothers: administer RhD immune globulin

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10. Summary Algorithm

Is induction indicated?
      ↓ Yes
Confirm gestational age ≥ 39 weeks (elective) OR outweighs risk (indicated)
      ↓
Assess Bishop score
      ↓
Score < 6 (unfavourable)?
   → YES: Cervical ripening first
         - PGE2: Dinoprostone gel (Prepidil) or insert (Cervidil)
         - PGE1: Misoprostol 25 µg vaginally q4h [avoid if prior C-section scar]
         - Mechanical: Foley catheter [preferred if prior C-section]
   → NO (Score ≥ 6, ripe cervix):
         - Amniotomy (if vertex engaged, cx ≥ 2 cm)
         - Oxytocin IV infusion (low-dose or high-dose protocol)
      ↓
Continuous EFM + uterine monitoring throughout
      ↓
Goal: Adequate active labour → Vaginal delivery
      ↓
If hyperstimulation or FHR non-reassuring → Resuscitate + consider C-section

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• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, Chapter 40 (Induction of Labor)
• Pfenninger and Fowler's Procedures for Primary Care, Chapter 163 (Labor Induction)
• Textbook of Family Medicine, 9th Edition, Chapter 20

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1. Cerviprime Gel

What it is

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Drug Profile

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Mechanism of Action

• Collagen fibres are broken down and remodelled
• Water content increases (cervix becomes softer, more pliable)
• Proteoglycans and glycosaminoglycans change in composition
• The cervix shortens (effaces) and begins to dilate

1. Directly softening the cervix - stimulates collagenase and matrix metalloproteinase release, breaking down collagen
2. Increasing cervical pliability - alters the composition of ground substance
3. Sensitizing the uterine myometrium to oxytocin, preparing it for contractions
4. Stimulating uterine contractions directly (though cervical effect is independent of contraction number)

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Dosing Protocol

1. Patient is placed in lithotomy position
2. Cervical status assessed (Bishop score measured)
3. 0.5 mg gel (the full 2.5 mL syringe) is placed into the cervical canal (intracervically) just below the internal os, using the provided catheter
4. Patient remains supine for 15-30 minutes after insertion to prevent gel leakage
5. EFM monitoring for minimum 2 hours after insertion
6. Repeat once after 6-12 hours if Bishop score has not changed appreciably
7. Maximum: 2 doses in 24 hours
8. If spontaneous labour does not start, oxytocin may be started after an interval

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Comparison: Cerviprime Gel vs Cervidil Insert

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Contraindications to Cerviprime

• Previous uterine surgery / caesarean section (relative - prostaglandins increase rupture risk)
• Active uterine contractions
• Fetal distress / non-reassuring CTG
• Active vaginal bleeding
• Ruptured membranes (if gel is to be placed intracervically - risk of infection)
• Hypersensitivity to prostaglandins
• Conditions where vaginal delivery is contraindicated (e.g. placenta praevia)

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Key Points About Cerviprime

• It acts primarily on cervical connective tissue - the ripening effect is independent of how many contractions it causes
• Misoprostol (PGE1) is more potent and cheaper; meta-analyses show misoprostol gives shorter time to delivery and lower C-section rate - but misoprostol cannot be removed and carries higher hyperstimulation risk
• Cerviprime/Prepidil is preferred over misoprostol in women with a prior caesarean scar (though still used with caution)
• Always have terbutaline 0.25 mg readily available before using Cerviprime, in case hyperstimulation occurs

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2. Uterine Hyperstimulation

Definition

More than 5 contractions in any 10-minute window (averaged over 30 minutes), OR contractions of moderate to strong intensity in >50% of contractions in a 10-minute segment.

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Two Patterns

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Why It's Dangerous

• Relaxation time between contractions is shortened or eliminated
• Intervillous blood flow is chronically reduced
• Fetal hypoxia and acidosis develop
• Placental abruption may occur (excessive pressure)
• Prolonged uterine hypertonus can cause uterine rupture (especially with prior scar)

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Causes

• Oxytocin - most common; dose-dependent; easily managed by reducing/stopping infusion
• Prostaglandins (misoprostol, dinoprostone) - cannot be reduced once administered
• Spontaneous - can occur in sensitized uteri (e.g. abruption, infection)
• Prior uterine scar (reduces uterine compliance)

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Management of Hyperstimulation

1. Stop or reduce the causative agent:
   • Turn off / reduce oxytocin infusion rate
   • Remove Cervidil insert (using retrieval string)
   • If misoprostol/Prepidil gel: cannot remove - proceed to pharmacological management
2. Lateral (left-lateral) positioning of the mother
   • Relieves aortocaval compression
   • Improves uteroplacental blood flow
3. IV fluid bolus - 1000 mL lactated Ringer's or normal saline
   • Treats hypotension, improves placental perfusion
4. Oxygen 10 L/min via non-rebreather face mask
   • Increases maternal pO2, improving fetal oxygenation
5. Tocolysis if contractions do not settle:
   • Terbutaline 0.25 mg subcutaneously (β2-agonist - relaxes uterine smooth muscle)
   • This is why terbutaline must be pre-stocked before any prostaglandin use
6. Continuous EFM assessment throughout
   • If FHR remains non-reassuring after resuscitation → immediate delivery (vaginal or caesarean section)

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Prevention

• Use correct doses of oxytocin and prostaglandins
• Never give oxytocin within 2 hours of last misoprostol dose
• Close monitoring with EFM during all inductions
• Have terbutaline available at bedside before starting prostaglandins
• If using oxytocin: titrate to the minimum effective dose

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3. Adequate Contractions

Clinical Definition (CTG/External Monitoring)

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Quantitative Definition - Montevideo Units (MvU)

Example:

• 4 contractions in 10 minutes, each with mean amplitude 55 mmHg
• MvU = 4 × 55 = 220 MvU → Adequate

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Clinical Significance

• If MvU < 200 → contractions inadequate → increase oxytocin
• If MvU ≥ 200 for 2+ hours with no cervical change → arrest of active phase → consider operative delivery

• No cervical change for 4 hours with adequate contractions (≥200 MvU measured by IUPC), OR
• No cervical change for 6 hours with oxytocin and inadequate uterine activity

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Oxytocin Goal Parameters

• Frequency: 2-3 minutes apart (3-5 per 10 min)
• Duration: 45-60 seconds
• Intensity: 50-75 mmHg on IUPC
• Resting tone: Normal (uterus completely relaxed between contractions)

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