# Induction of Labor: Indications, Methods, and Management

## Overview

Induction of labor is the stimulation of uterine contractions before spontaneous labor onset to achieve vaginal delivery. Approximately 25 to 30% of all deliveries in the United States involve induction, a rate that has increased significantly over the past two decades.

## Indications

### Medical/Obstetric Indications

Medical and obstetric indications for induction include preeclampsia and gestational hypertension, gestational or pregestational diabetes (with timing varying by glycemic control and complications), premature rupture of membranes at term (PROM), oligohydramnios, fetal growth restriction, cholestasis of pregnancy, stable partial placental abruption, chronic hypertension, alloimmunization, post-term pregnancy (at or beyond 41 weeks), fetal demise, and chorioamnionitis.

### Elective Induction

Elective induction before 39 weeks was historically discouraged. The ARRIVE trial in 2018 changed practice for nulliparous women at 39 weeks, demonstrating that elective induction actually reduces cesarean rates (discussed below). Logistic or psychosocial indications may be reasonable at 39 weeks or later after appropriate counseling.

### Contraindications to Induction

Contraindications include placenta previa or vasa previa, prior classical or T-shaped uterine incision, active genital herpes lesion, transverse lie, umbilical cord prolapse, and prior myomectomy with entry into the uterine cavity (relative, with institution-dependent practice).

## Pre-Induction Assessment

### Bishop Score

The Bishop score assesses cervical readiness and predicts the likelihood of successful induction. It incorporates five components: dilation, effacement, station, consistency, and position. A Bishop score of 8 or greater indicates a favorable cervix with a high success rate using oxytocin alone. A Bishop score below 6 indicates an unfavorable cervix, and cervical ripening is recommended before starting oxytocin. The Bishop score is the strongest predictor of induction success.

### Other Assessments

Additional assessments before induction include confirming gestational age (39 weeks or greater for elective induction), verifying vertex presentation, estimating fetal weight, reviewing GBS status and the plan for prophylaxis, and assessing membrane status.

<image>Illustrated table of the Bishop Score components with visual representations of cervical dilation, effacement percentage, fetal station, cervical consistency, and cervical position, with scoring criteria for each factor</image>

## Cervical Ripening Methods

### Prostaglandins

#### Misoprostol (Cytotec) -- PGE1

Misoprostol can be administered by several routes. Vaginal administration of 25 mcg every 3 to 6 hours has the most supporting evidence. Oral administration of 25 to 50 mcg every 4 hours, with low-dose oral regimens increasingly used, is an alternative. Buccal and sublingual routes at 25 mcg are also available. Misoprostol is effective and inexpensive but is contraindicated in patients with a prior cesarean delivery due to the increased risk of uterine rupture. Tachysystole occurs in 5 to 10% of cases and is managed by removal of the vaginal tablet (if applicable) and terbutaline administration. Once administered vaginally, misoprostol cannot be removed and must be allowed to clear.

#### Dinoprostone (Cervidil/Prepidil) -- PGE2

Cervidil is a vaginal insert containing 10 mg of dinoprostone with controlled release over 12 hours. It can be removed if tachysystole occurs. Prepidil is an endocervical gel containing 0.5 mg, which can be repeated in 6 hours to a maximum of 3 doses. Dinoprostone is more expensive than misoprostol. It can be used in patients with a prior cesarean delivery according to some guidelines, though practice varies. After removal of Cervidil, a 30-minute wait is required before starting oxytocin. After Prepidil, a 6 to 12 hour wait is recommended.

### Mechanical Methods

#### Foley Catheter (Transcervical Balloon)

A 16 to 18 French Foley catheter is placed through the cervix with the balloon inflated with 30 to 60 mL of saline. It exerts mechanical pressure on the internal os and also stimulates local prostaglandin release. The Foley catheter is effective for cervical ripening, with vaginal delivery rates comparable to those achieved with prostaglandins. It is safe in patients with prior cesarean delivery, making it the preferred ripening method in this population. The catheter falls out when the cervix dilates to 3 to 4 cm, indicating successful ripening. It can be combined with misoprostol or oxytocin for faster ripening.

#### Double-Balloon Catheter (Cook Cervical Ripening Balloon)

The double-balloon catheter has two balloons: one positioned above and one below the internal os, each inflated with 80 mL. It has similar efficacy to the single-balloon Foley and may be more comfortable for patients.

| Ripening Method | Agent/Device | Dosing | Interval | Prior Cesarean? |
|---|---|---|---|---|
| Misoprostol (PGE1) | Vaginal | 25 mcg q3-6h | Wait before oxytocin | Contraindicated |
| Misoprostol (PGE1) | Oral | 25-50 mcg q4h | Wait before oxytocin | Contraindicated |
| Dinoprostone (Cervidil) | Vaginal insert | 10 mg over 12 hrs | 30 min before oxytocin | Varies by institution |
| Dinoprostone (Prepidil) | Endocervical gel | 0.5 mg q6h (max 3 doses) | 6-12 hrs before oxytocin | Varies by institution |
| Foley catheter | Transcervical balloon | 30-60 mL inflation | Can start oxytocin concurrently | Safe |
| Double-balloon catheter | Cook catheter | 80 mL each balloon | Can start oxytocin concurrently | Safe |

### Combination Approaches

Combining a Foley catheter with misoprostol achieves faster time to delivery than either method alone and is increasingly used. Combining a Foley catheter with oxytocin is another effective approach for an unfavorable cervix. However, concurrent misoprostol and oxytocin is not recommended because of the excessive risk of tachysystole.

## Oxytocin Protocols

### Low-Dose (Physiologic)

The low-dose protocol uses a starting dose of 0.5 to 2 mU/min with increments of 1 to 2 mU/min every 30 to 40 minutes. It produces a lower tachysystole rate but may result in a longer time to delivery.

### High-Dose

The high-dose protocol uses a starting dose of 4 to 6 mU/min with increments of 4 to 6 mU/min every 15 to 40 minutes. It achieves a shorter time to delivery with a higher tachysystole rate but has not demonstrated increased adverse neonatal outcomes in studies. The maximum dose varies by institution, typically 20 to 40 mU/min.

### Monitoring During Oxytocin

Continuous electronic fetal monitoring is required. Contraction frequency is assessed with a goal of 3 to 5 contractions in 10 minutes. When an intrauterine pressure catheter (IUPC) is placed, Montevideo units of 200 or greater are the target. Tachysystole, defined as more than 5 contractions in 10 minutes, is managed differently based on fetal heart rate findings. With FHR changes, oxytocin is reduced or stopped, the patient is repositioned laterally, an IV fluid bolus is given, and terbutaline 0.25 mg subcutaneously is considered. Without FHR changes, oxytocin is reduced and the patient is observed.

### Oxytocin Pharmacology

Oxytocin has an IV onset of 3 to 5 minutes, a half-life of 3 to 12 minutes, and reaches steady state 20 to 40 minutes after a dose change. It has an ADH-like effect that causes water retention, creating a risk of water intoxication with prolonged infusion and hypotonic fluids; isotonic fluids should therefore be used. Receptor desensitization can occur with prolonged administration.

<image>Flowchart for induction of labor method selection based on Bishop score and patient history, showing pathways from unfavorable cervix (Bishop <6) to cervical ripening options (prostaglandins, mechanical, combination) and from favorable cervix (Bishop >=8) directly to oxytocin, with special considerations for prior cesarean patients</image>

## ARRIVE Trial

### Study Design

The ARRIVE trial was a randomized controlled trial published in 2018 by Grobman et al. It randomized low-risk nulliparous women to elective induction at 39 weeks versus expectant management.

### Key Findings

Elective induction at 39 weeks reduced the cesarean delivery rate (18.6% versus 22.2%, relative risk 0.84), reduced hypertensive disorders (9.1% versus 14.1%), and did not increase adverse neonatal outcomes, with a modest decrease in NICU admissions. These findings do not apply to multiparous women or high-risk patients, who represent a different population.

### Clinical Implications

ACOG supports offering induction at 39 weeks to low-risk nulliparous women after informed discussion. The decision should be shared between the patient and provider and is not mandated. Adequate hospital resources and staffing are required.

## Special Situations

### Induction After Prior Cesarean (TOLAC)

Misoprostol is contraindicated in patients with a prior cesarean delivery due to increased uterine rupture risk. Mechanical ripening with a Foley catheter is acceptable. Oxytocin may be used for augmentation with close monitoring. Dinoprostone use varies by institution, with some allowing it and others avoiding it.

### Induction for Fetal Demise

Misoprostol is the primary agent, with higher doses acceptable (200 to 400 mcg vaginally every 4 to 6 hours). Mifepristone 200 mg orally given 24 to 48 hours before misoprostol improves efficacy. Mechanical dilation with a Foley catheter or laminaria serves as an adjunct. Higher misoprostol doses are used in the second trimester.

### Prolonged Latent Phase During Induction

Adequate time must be allowed, as the latent phase during induction can be very prolonged. ACOG recommends cervical ripening plus oxytocin for at least 12 to 18 hours (some centers allow 24 hours) before declaring a failed induction. A failed induction should only be diagnosed if it is impossible to generate regular contractions and cervical change despite adequate ripening and oxytocin administration.

## Clinical Pearls

The Bishop score is the best predictor of induction success and should be assessed before choosing an induction method.

The Foley catheter is the safest cervical ripening method for patients with a prior cesarean delivery.

Misoprostol is contraindicated in TOLAC patients.

Combination ripening with a Foley catheter plus misoprostol shortens time to delivery without increasing complications.

The ARRIVE trial supports offering 39-week induction to low-risk nulliparous women. It reduces, rather than increases, cesarean rates.

Do not declare a failed induction too early. At least 12 to 18 hours of ripening plus oxytocin should be allowed before labeling an induction as failed.

Concurrent oxytocin and misoprostol should be avoided because of the excessive stimulation risk.

Always start with cervical ripening if the Bishop score is below 6. Proceeding directly to oxytocin with an unfavorable cervix will likely fail.

## References

- ACOG Practice Bulletin No. 107: Induction of Labor (2009, reaffirmed 2022)
- Grobman WA et al. Labor induction versus expectant management in low-risk nulliparous women (ARRIVE). N Engl J Med. 2018;379:513-523
- ACOG Committee Opinion No. 766: Approaches to Limit Intervention During Labor and Birth (2019)
- Ten Eikelder MLG et al. Induction of labor at term with oral misoprostol versus a Foley catheter: systematic review. BMJ. 2016;353:i2838
- Levine LD et al. Combination of Foley catheter plus misoprostol vs misoprostol alone for cervical ripening: the FOLD randomized trial. JAMA. 2020