What is the recommended protocol for inducing labor at ≥37 weeks gestation, including assessment of cervical favorability, selection and dosing of cervical ripening agents, oxytocin regimen, and fetal and uterine monitoring?

Labor Induction Protocol at ≥37 Weeks Gestation

For labor induction at ≥37 weeks, begin by assessing the Bishop score: if <5, use cervical ripening (dinoprostone 10 mg vaginal insert for up to 12 hours OR oral misoprostol 20-25 µg every 2-6 hours if no prior cesarean), wait 30 minutes after ripening completion, then start oxytocin with continuous fetal and uterine monitoring, and allow at least 12 hours after completing ripening, membrane rupture, and oxytocin before declaring failed induction. 1

Step 1: Cervical Assessment

• Measure the Bishop score to determine cervical favorability before selecting your induction method 1
• Bishop score <5 = unfavorable cervix requiring cervical ripening before oxytocin can be effective 1
• Bishop score ≥5 = favorable cervix permitting immediate oxytocin infusion and artificial rupture of membranes without prior ripening 1
• Transvaginal ultrasound offers no predictive advantage over Bishop score for labor induction outcomes 1

Step 2: Cervical Ripening (When Bishop Score <5)

First-Line Options:

Dinoprostone (Prostaglandin E₂):

• Use a single 10 mg vaginal insert releasing approximately 0.3 mg/hour 1
• Maximum duration is 12 hours 1
• Wait at least 30 minutes after removing dinoprostone before starting oxytocin 1
• Requires continuous fetal heart rate and uterine activity monitoring throughout administration 1

Oral Misoprostol (Cost-Effective Alternative):

• Dose: 20-25 µg every 2-6 hours 1
• Results in fewer cesarean sections (RR 0.84) and costs significantly less than dinoprostone 1
• Absolutely contraindicated in women with prior cesarean delivery due to approximately 13% uterine rupture risk 1, 2

Mechanical Method (Foley Catheter):

• Use 60-80 mL single-balloon Foley catheter for 12 hours 3
• Preferred in patients with cardiac disease, cyanosis, or active cardiovascular conditions to avoid systemic vascular resistance drops 1, 4

Step 3: Oxytocin Regimen

• Start oxytocin infusion at increasing rates from 1-3 mIU/min to a maximal rate of 36 mIU/min at 15-40 minute intervals 5
• At infusion rates of 20-30 mIU/min, plasma oxytocin concentration increases approximately 2-3 fold above basal level 5
• Consider discontinuing oxytocin once 5-6 cm cervical dilation is achieved if adequate contractions are present 3
• Total oxytocin given during labor typically ranges from 5-10 IU 5

Step 4: Amniotomy Timing

• Reserve amniotomy as an adjunctive measure, not a primary intervention 1
• Can be performed once Bishop score ≥5 is achieved 1
• For term prelabor rupture of membranes, start oxytocin immediately (as soon as feasible) or up to 12 hours if labor is not evident 3

Step 5: Monitoring Requirements

• Continuous fetal heart rate monitoring throughout dinoprostone administration and oxytocin infusion 1
• Continuous uterine activity monitoring to detect tachystole or overstimulation 1
• Monitor cervical dilation every 2-4 hours and plot progress to detect arrest patterns early 1
• Palpate fetal skull base suprapubically to differentiate true descent from molding 1

Step 6: Defining Failed Induction

Critical timing rule: Allow at least 12 hours after completion of cervical ripening, membrane rupture, and oxytocin use before considering cesarean delivery for "failed induction" in the latent phase 1

• Nulliparous women require longer induction times (often 24+ hours total) 1
• Multiparous women progress faster with dilation rates ≥1.5 cm/hour 1
• Do not declare failed induction before 15 hours of oxytocin infusion and amniotomy if feasible, ideally after 18-24 hours 3

Critical Contraindications

Absolute Contraindications to Dinoprostone:

• Active cardiovascular disease due to profound blood pressure effects, theoretical risk of coronary vasospasm, and arrhythmias 1, 4
• Use mechanical methods (Foley catheter) instead in these patients 1, 4

Absolute Contraindications to Misoprostol:

• Prior cesarean delivery due to significantly increased uterine rupture risk (approximately 13%) 1, 2
• Advanced liver failure due to hepatic metabolism 4

Relative Considerations:

• Patients with asthma can use prostaglandin E₂ with appropriate monitoring 1
• For severe peanut allergy, use vaginal gel formulations of prostaglandin E₂ rather than capsule forms containing peanut oil 1

Special Population: Anticoagulation

• Patients on therapeutic anticoagulation require switching to unfractionated heparin at least 36 hours before planned induction 1
• Discontinue heparin 4-6 hours before delivery 1
• Women on prophylactic low-molecular-weight heparin should be allowed spontaneous labor rather than scheduled induction when possible 4

Common Pitfalls to Avoid

• Do not initiate oxytocin when Bishop score is <5 without first performing cervical ripening; oxytocin alone is ineffective in this setting 1
• Do not declare failed induction before the mandatory 12-hour observation period after ripening, membrane rupture, and oxytocin 1
• Do not perform elective induction before 39 weeks 0 days gestation due to increased respiratory morbidity 1, 4, 2
• Do not use misoprostol in women with prior uterine surgery 1, 2
• Suspected fetal macrosomia alone is not an indication for induction, as it doubles cesarean risk without reducing shoulder dystocia or neonatal morbidity 1, 4

Mechanical Causes of Failed Induction to Assess

• Cephalopelvic disproportion (CPD) accounts for roughly 25-30% of protracted active-phase labor 1
• Fetal malposition (occiput posterior or transverse) and malpresentation (brow) are associated with delayed progress 1
• Maternal obesity, diabetes, and fetal macrosomia increase CPD risk 1
• Assess for excessive molding, deflexion, or asynclitism; their presence signals mechanical obstruction that may necessitate cesarean delivery 1