What prostaglandin (e.g., dinoprostone or misoprostol) should be used to improve a low Bishop score, how should it be administered for cervical ripening, and what are its potential side effects?

Misoprostol for Cervical Ripening: Dosing, Administration, and Side Effects

For improving an unfavorable Bishop score, use oral misoprostol solution 20–25 µg every 2–6 hours as the preferred first-line pharmacological method, which results in fewer cesarean sections and lower uterine hyperstimulation rates compared to dinoprostone. 1

Optimal Dosing Regimen

• Oral route: Administer misoprostol solution 20–25 µg every 2–6 hours, which is the preferred non-vaginal approach endorsed by current guidelines. 1, 2

• Vaginal route (alternative): Use 25 µg every 3–6 hours if oral administration is not feasible; this achieves a median time to vaginal delivery of 20.1 hours. 2

• Avoid higher doses: The 50 µg regimen carries markedly increased risk of uterine hyperstimulation and should only be considered in highly select cases with extreme caution. 1

• Lower doses are safer: Oral misoprostol causes 31% less hyperstimulation than vaginal administration (RR 0.69). 2

Step-by-Step Administration Protocol

1. Assess Bishop score to confirm cervical unfavorability (score <5 indicates need for ripening). 3

2. Screen for absolute contraindications:

   • Prior cesarean delivery or any uterine surgery (13% rupture risk with misoprostol versus 1.1% with oxytocin). 1, 2, 4
   • Active cardiovascular disease (use mechanical methods instead). 1
   • Grand multiparity (increased rupture risk). 4

3. Administer first dose of oral misoprostol 20–25 µg. 1, 2

4. Initiate continuous monitoring of fetal heart rate and uterine activity starting 30 minutes to 2 hours after the first dose and maintain throughout induction. 1, 2

5. Repeat dosing every 2–6 hours only if:

   • Bishop score remains <6
   • No spontaneous membrane rupture
   • No active labor
   • No excessive uterine activity (>5 contractions per 10 minutes). 1

6. If oxytocin augmentation is needed, wait at least 30 minutes after the last misoprostol dose before starting oxytocin infusion. 1, 3

7. If cervical ripening fails after appropriate dosing, transition to mechanical methods (Foley catheter) or consider cesarean delivery rather than escalating the misoprostol dose. 1, 3

Side Effects and Complications

Common Adverse Effects

• Uterine tachysystole: Defined as >5 contractions per 10 minutes; occurs less frequently with the 25 µg dose compared to higher doses or dinoprostone. 1, 5

• Meconium-stained amniotic fluid: More frequent with misoprostol (27.9%) compared to dinoprostone (10.5%) in one trial, though another study found thick meconium more common with oral misoprostol. 5, 6

• Gastrointestinal effects: Diarrhea, nausea, and abdominal cramping may occur due to prostaglandin effects. 4

Serious Complications (Primarily When Contraindications Ignored)

• Uterine rupture: Risk escalates to 13% in women with prior cesarean delivery, compared to 1.1% with oxytocin and 2% with prostaglandin E2. 1, 2, 4

• Uterine hyperstimulation with fetal compromise: May progress to uterine tetany with marked impairment of uteroplacental blood flow, leading to adverse fetal heart rate changes. 4

• Maternal complications: Uterine rupture requiring surgical repair, hysterectomy, salpingo-oophorectomy, amniotic fluid embolism, maternal shock, and in rare cases maternal death. 4

• Fetal complications: Fetal bradycardia, fetal distress, and fetal death have been reported. 4

• Cesarean delivery: Increased risk when hyperstimulation occurs, particularly with higher doses (50 µg regimen showed significantly more cesarean deliveries due to hyperstimulation). 7

High Fever Syndrome (Postpartum Use)

• When misoprostol is used for postpartum hemorrhage management, high fevers >40°C (104°F) accompanied by tachycardia, disorientation, agitation, and convulsions have been reported; these fevers are transient and require supportive therapy. 4

Critical Contraindications (Absolute)

• Prior cesarean delivery or major uterine surgery: This is an absolute contraindication based on Level B evidence from ACOG; the 13% rupture risk is unacceptably high. 1, 2, 4

• Multiple prior cesarean sections: Women with three prior cesarean sections face catastrophic rupture risk even with a single 25 µg dose. 2

• Active cardiovascular disease: Use mechanical methods (Foley catheter) instead to avoid systemic vascular resistance drops. 1

• Cyanotic heart disease: Mechanical methods are preferred. 1

Advantages Over Dinoprostone

• Cost: Misoprostol costs $0.36–$1.20 per 100 µg tablet versus $65–$75 for dinoprostone gel or $165 for the dinoprostone insert. 1

• Storage: Misoprostol remains stable at room temperature and does not require refrigeration, unlike dinoprostone. 1

• Efficacy: Oral misoprostol 20–25 µg results in fewer cesarean sections (RR 0.84) compared to dinoprostone. 1, 3

• Induction time: Misoprostol shortens the insertion-to-delivery interval by 3.91 hours on average compared to dinoprostone. 8

Common Pitfalls to Avoid

• Never use misoprostol in women with prior cesarean delivery—the rupture risk is unacceptably high and this is an absolute contraindication. 1, 2, 4

• Do not escalate to higher doses if cervical ripening fails; instead, switch to mechanical methods or proceed to cesarean delivery. 1, 3

• Avoid starting oxytocin too soon after misoprostol; wait at least 30 minutes after the last dose. 1, 3

• Do not continue prolonged induction attempts with an unfavorable cervix; transition to alternative methods to reduce maternal and fetal risk. 1, 3

• Ensure continuous monitoring is in place before administering the first dose and maintained throughout to promptly detect tachysystole and fetal distress. 1, 2