Key Facts

Induction of labour is the process of artificially stimulating uterine contractions to achieve vaginal delivery before spontaneous onset of labour. It is one of the most commonly performed obstetric interventions.

Epidemiology

• IOL rate in the UK: approximately 33% of all births (rising trend)
• Most common indication: post-dates pregnancy (>41 weeks)
• Success rate for vaginal delivery after IOL: approximately 70-80%

Aetiology (Indications)

• Post-dates pregnancy (≥41+0 weeks) - most common
• Pre-eclampsia / gestational hypertension
• Diabetes (gestational or pre-existing)
• Fetal growth restriction
• PROM at term (>24 hours without spontaneous onset)
• Obstetric cholestasis
• Multiple pregnancy
• Maternal request (after 39 weeks following counselling)
• Intrauterine fetal death

Pathophysiology

• Prostaglandins (PGE2, PGE1) cause cervical ripening through collagenase activation and increase in hyaluronic acid
• Prostaglandins also stimulate myometrial contractions
• Oxytocin stimulates uterine contractions via oxytocin receptors (upregulated at term)
• Amniotomy releases prostaglandins from the membranes and increases local oxytocin release

Pre-induction Assessment

• Confirm indication and gestation
• Assess Bishop score (cervical dilatation, effacement, consistency, position, station)
• Confirm fetal presentation (cephalic)
• Baseline CTG
• Exclude contraindications

During Induction

• Onset of regular uterine contractions
• Progressive cervical dilatation
• Spontaneous or artificial rupture of membranes

Red Flags / Complications

• Uterine hyperstimulation: >5 contractions in 10 minutes with or without fetal heart rate changes
• Pathological CTG
• Cord prolapse (particularly after ARM with high presenting part)
• Uterine rupture (especially with previous CS)
• Failed induction (failure to establish labour after full IOL process)

Bedside

• Modified Bishop score assessment (vaginal examination)
• CTG (baseline and during IOL)
• Blood pressure, temperature, pulse
• Confirm fetal presentation (palpation ± ultrasound)

Bloods

• Group and save
• FBC if clinically indicated
• U&Es, LFTs if pre-eclampsia is the indication

Imaging

• Ultrasound for fetal presentation confirmation, liquor volume, EFW if indicated

Special Tests

• None routinely required beyond Bishop score

Non-pharmacological

• Membrane sweep: offered from 40 weeks in nulliparous and 41 weeks in multiparous (NICE NG207); reduces need for formal IOL
• Mechanical cervical ripening: Foley catheter balloon (30-80mL) or double balloon catheter inserted through cervix
• Amniotomy (ARM): performed when cervix sufficiently dilated (Bishop ≥6)

Pharmacological

• Vaginal prostaglandins (cervical ripening if Bishop <6):
  • Dinoprostone (PGE2): 2mg gel or 10mg controlled-release pessary (Propess), repeat gel at 6 hours if needed
  • Misoprostol (PGE1): 25-50mcg vaginal (lower dose if previous CS)
• Oxytocin infusion (after ARM, for augmentation): start at 1-2 mU/min, increase every 30 minutes to max 32 mU/min
• Tocolysis for hyperstimulation: remove Propess pessary, terbutaline 250mcg SC or salbutamol nebuliser

Surgical/Interventional

• ARM performed with amnihook when cervix favourable
• Instrumental delivery or CS if required during IOL
• Emergency CS for failed IOL, fetal compromise, or uterine rupture

Referral Criteria

• Failed IOL: consultant obstetrician review to discuss options (further attempt, caesarean section)
• Uterine hyperstimulation not responding to simple measures
• Abnormal CTG: senior obstetric and midwifery review

• Success rate for vaginal delivery after IOL: 70-80% overall
• Bishop score >6: >90% success for vaginal delivery
• Bishop score <3: higher CS rate (~30-40%)
• IOL at 41 weeks reduces perinatal mortality without increasing CS rate (NICE NG207)
• Uterine hyperstimulation: 1-5% (higher with prostaglandins)
• Uterine rupture with IOL in previous CS: approximately 0.5% (higher with prostaglandins than mechanical methods)
• Cord prolapse after ARM: <1%

Modified Bishop Score

Key Trials