What are the methods to induce labour?

Methods to Induce Labour

For labour induction with a favourable cervix, use oxytocin with artificial rupture of membranes; for an unfavourable cervix, use oral misoprostol solution 20-25 µg every 2-6 hours as the preferred pharmacological method, or mechanical methods (Foley catheter) in high-risk cardiac or cyanotic patients. 1, 2

Cervical Assessment First

• Assess the Bishop score (cervical dilatation, effacement, consistency, position, and fetal station) to determine cervical favourability before selecting an induction method 1
• A favourable Bishop score indicates readiness for oxytocin and membrane rupture, while an unfavourable cervix requires cervical ripening first 1

Primary Induction Methods

For Favourable Cervix

• Oxytocin infusion with artificial rupture of membranes is the standard approach when the cervix is favourable 1, 3
• Oxytocin dosing: Start at 1-2 mU/min IV, increase gradually by 1-2 mU/min increments until achieving a contraction pattern similar to normal labour 3
• Prepare by combining 10 units oxytocin in 1000 mL non-hydrating physiologic electrolyte solution (10 mU/mL concentration) 3
• Requires continuous fetal heart rate and uterine contraction monitoring with accurate infusion pump control 3

For Unfavourable Cervix: Pharmacological Options

Oral Misoprostol (Preferred)

• Use 20-25 µg oral misoprostol solution every 2-6 hours as the optimal regimen, which results in fewer cesarean sections and lower uterine hyperstimulation rates compared to higher doses 2
• Oral route is superior to vaginal administration, with lower hyperstimulation rates (RR 0.69) and fewer cesarean sections compared to vaginal dinoprostone (RR 0.84) 2
• Requires continuous fetal heart rate and uterine activity monitoring from 30 minutes to 2 hours after each dose 2
• Major cost advantage: $0.36-$1.20 per 100 µg tablet versus $65-$75 for dinoprostone gel or $165 for dinoprostone insert 2
• Stable at room temperature, eliminating refrigeration requirements 2

Dinoprostone (Prostaglandin E2)

• Dinoprostone vaginal insert (10 mg) or gel can be used for cervical ripening 4, 5
• The vaginal insert can be safely used for up to 24 hours, though most tachysystole cases (68%) occur within 12 hours 5
• In low-risk pregnancies, dinoprostone achieves 67.6% vaginal delivery rates 4
• Vaginal misoprostol appears more effective than dinoprostone insert for premature rupture of membranes, with shorter time to active labour (7 vs 11 hours) and delivery within 24 hours (88.4% vs 58.0%) 6

For Unfavourable Cervix: Mechanical Methods

• Foley catheter is preferable to pharmacological agents in patients with cyanosis, active cardiovascular disease, or conditions where drops in systemic vascular resistance or blood pressure would be detrimental 1
• Mechanical methods avoid the hemodynamic effects of prostaglandins 1

Critical Contraindications and Safety Considerations

Absolute Contraindications

• Misoprostol is absolutely contraindicated in women with previous cesarean delivery due to 13% uterine rupture risk, substantially higher than oxytocin (1.1%) or prostaglandin E2 (2%) 2, 7
• The American College of Obstetricians and Gynecologists advises avoiding misoprostol entirely in this population 2
• Dinoprostone is contraindicated in active cardiovascular disease due to profound blood pressure effects 1

Special Population Considerations

• In women with advanced liver failure, misoprostol may be less suitable as it requires hepatic metabolism to convert from E1 to active E2 prostaglandin; consider alternative methods 2
• In cardiac patients or those with cyanosis, mechanical methods (Foley catheter) are preferred over prostaglandins to avoid systemic vascular resistance drops 1
• Prostaglandin E2 carries theoretical risk of coronary vasospasm and low risk of arrhythmias 1

Uterine Rupture Risk Stratification

• Oxytocin in prior cesarean: 1.1% rupture risk 7
• Prostaglandin E2 in prior cesarean: 2% rupture risk 1
• Misoprostol in prior cesarean: 13% rupture risk 2
• Induction decreases likelihood of successful vaginal birth after cesarean compared to spontaneous labour 7

Monitoring Requirements

• Continuous fetal heart rate and uterine activity monitoring is mandatory during all pharmacological induction methods 2, 3
• For oxytocin: Monitor fetal heart rate, resting uterine tone, and frequency/duration/force of contractions 3
• Discontinue infusion immediately if uterine hyperactivity or fetal distress occurs; administer oxygen to mother 3

Common Pitfalls to Avoid

• Avoid prolonged induction time when cervix is unfavourable - consider mechanical methods or cesarean delivery if cervical ripening fails 1
• Do not use misoprostol in women with prior cesarean - the rupture risk is unacceptably high 2
• Avoid dinoprostone in active cardiovascular disease due to blood pressure effects 1
• Do not use general anesthesia if possible, particularly in respiratory disease patients 1

Adjunctive Considerations

• Prostaglandin E2 for induction or oxytocin for augmentation has not been associated with worsening lung function or asthma exacerbation 1
• Early epidural analgesia is preferred for pain relief and can be extended for emergency cesarean if needed 1
• Active management of third stage with oxytocin is preferred over ergotamine (which may cause bronchospasm) 1