When to Start Induction of Labor

1. Indicated (Medically Necessary) Induction

Maternal Indications

• Pregnancy-related hypertension (gestational hypertension, preeclampsia)
• Chorioamnionitis (intrauterine infection)
• Fetal death (intrauterine fetal demise)
• Uncontrolled maternal diabetes
• Severe maternal cardiac, renal, or pulmonary disease

Fetal Indications

• Postterm pregnancy (beyond 41-42 weeks), especially with oligohydramnios
• Diabetes mellitus (with fetal macrosomia or poor glycemic control)
• Intrauterine growth restriction (IUGR) with fetal jeopardy on testing
• Isoimmunization (Rh or other antibody disease with fetal compromise)
• Premature rupture of membranes (PROM) at or near term (established fetal maturity)
• Hypertensive complications of pregnancy

Logistic/Social Indications (select cases)

• Significant distance from the hospital
• History of very rapid (precipitous) labors
• These are acceptable only when gestational age ≥39 weeks is confirmed

2. Gestational Age Requirements

• Early positive pregnancy test
• Early ultrasound (ideally before 20 weeks)
• Early fetal heart tone auscultation
• In some cases, amniotic fluid fetal lung maturity testing

3. Cervical Readiness - The Bishop Score

• Bishop score ≥ 6 (or ≥ 9 by some criteria): Cervix is favorable - proceed with induction (amniotomy + oxytocin)
• Bishop score < 6: Cervix is unfavorable - cervical ripening is needed first (with prostaglandins or mechanical methods) before induction is started

4. Contraindications - When NOT to Induce

Absolute Contraindications

• Placenta previa or placenta accreta
• Acute severe fetal distress (immediate cesarean needed)
• Shoulder (transverse) presentation
• Floating (unengaged) presenting part
• Prior uterine surgery that precludes trial of labor (e.g., classical cesarean)
• Uncontrolled hemorrhage

Relative Contraindications

• Grand multiparity (5+ prior pregnancies beyond 20 weeks)
• Multiple gestation (twins/triplets)
• Suspected cephalopelvic disproportion (CPD)
• Breech presentation
• Inability to continuously monitor fetal heart rate during labor

5. Quick Summary - Decision Framework

Is there a medical/fetal indication?
    YES → Is gestational age appropriate + no contraindications?
              YES → Check Bishop score
                        ≥6 → Proceed with induction (amniotomy ± oxytocin)
                        <6 → Cervical ripening first, then induction
              NO → Re-evaluate timing
    NO → Is GA ≥ 39 weeks? → Elective induction may be offered (shared decision)

• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice (sections on Induction of Labor and Indicated Induction)
• Textbook of Family Medicine 9e, p. 505

Induction of Labor Protocols

Step 1 - Pre-Induction Assessment

1. Confirm gestational age (≥39 weeks for elective)
2. Perform a nonstress test (NST) - if nonreactive or contractions already present, do NOT proceed
3. Calculate the Bishop score (see table from previous answer)
4. Obtain IV access
5. Ensure continuous external fetal heart rate (FHR) and uterine contraction monitoring is available
6. Document informed consent

Step 2 - Cervical Ripening (if Bishop Score < 6)

A. Mechanical Methods

Foley Catheter (most commonly used)

1. Using sterile technique, insert a 16-26 Fr Foley catheter through the endocervix into the space between the amniotic membrane and the lower uterine segment
2. Inflate the balloon with 30-50 mL of normal saline
3. Retract the balloon so it rests against the internal os
4. Apply gentle tension (constant by suspending 1L IV fluid from the catheter end, or intermittent with a gentle tug 2-4 times/hour)
5. Remove the catheter after 6 hours or when it falls out spontaneously (indicating cervical dilation ~3-4 cm)

• Advantage: Can be used in patients with prior cesarean section; lower hyperstimulation risk than prostaglandins

Laminaria (osmotic dilators)

1. Insert laminaria of appropriate size so its tip rests against the internal os
2. Laminaria swells 3-4 fold over 4-6 hours by absorbing cervical water, causing mechanical dilation
3. Remove after 4-6 hours, reassess cervix; may repeat with larger laminaria if cervix still unfavorable

B. Pharmacologic - Prostaglandins

1. Dinoprostone Gel (Prepidil) - PGE2

• Dose: 0.5 mg in 2.5 mL gel, placed intracervically
• Catheter: 20 mm if <50% effacement; 10 mm if >50% effacement
• Technique: Patient in dorsal position; instill gel just below the internal os
• Post-insertion: Patient remains supine 15-30 min; monitor FHR + contractions for 2 hours
• Repeat: Every 6 hours if minimal change; max 1.5 mg (3 doses) in 24 hours
• Oxytocin interval: Wait 6-12 hours (minimum 4 hours if no hyperstimulation) before starting oxytocin

2. Dinoprostone Insert (Cervidil) - PGE2

• Dose: 10 mg controlled-release vaginal insert in posterior fornix
• Duration: Leave in place up to 12 hours or until active labor begins
• Post-insertion: Supine for 2 hours then ambulatory; continuous FHR monitoring for 2 hours
• Key advantage: The insert has a retrieval string - can be immediately removed if uterine hyperstimulation occurs
• Oxytocin interval: Remove insert at least 30 minutes before starting oxytocin

3. Misoprostol (Cytotec) - PGE1 (off-label)

• Dose: 25 mcg intravaginally (1/4 of a 100 mcg tablet) into the posterior vaginal fornix
• Repeat: Every 4 hours if minimal cervical change; hold if:
  • ≥2 contractions in 10 minutes
  • Bishop score ≥8 achieved
  • Active labor begins
  • Non-reassuring FHR
• Maximum duration: 24 hours
• Oxytocin interval: Do NOT start oxytocin sooner than 2 hours after last misoprostol dose
• Oral alternative: 100 mcg orally every 3-4 hours (also effective)
• CONTRAINDICATED in women with prior cesarean section (uterine rupture risk)

Step 3 - Induction (Favorable Cervix or After Ripening)

A. Amniotomy (AROM)

• Preferred method when cervix is favorable (Bishop ≥6) and vertex is well engaged
• Performed using an amnihook under sterile conditions
• If labor does not follow within a reasonable interval, oxytocin infusion is added
• Carries a risk of cord prolapse if the presenting part is not well engaged

B. Oxytocin (Pitocin) - The Main Induction Agent

• 10,000-20,000 mU oxytocin diluted in 1 L lactated Ringer's or normal saline
• This gives a 10-20 mU/mL concentration
• Administered via infusion pump only - never freeflow

• Contractions every 2-3 minutes
• Duration 45-60 seconds
• Intensity 50-75 mmHg
• Normal resting tone between contractions

• ~90% of patients respond to ≤16 mU/min
• Rarely requires >20-40 mU/min
• Steady-state levels reached about 40 minutes after starting/changing infusion rate
• At doses >20 mU/min, oxytocin has antidiuretic (vasopressin-like) effects - risk of water intoxication and hyponatremia if given in large volumes of hypotonic fluid
• High-dose protocols reduce cesarean rate for dystocia in nulliparas ("Active Management of Labor")

Monitoring During Induction

• Continuous electronic FHR monitoring throughout labor
• Watch for uterine hyperstimulation (tachysystole: >5 contractions in 10 min)
• If hyperstimulation occurs:
  • Stop or reduce oxytocin
  • Remove dinoprostone insert (if being used)
  • Administer terbutaline 0.25 mg SC as tocolytic (should be prepared in advance)

Practical Tips

• Cervical ripening can be started in the evening/overnight so that amniotomy/oxytocin can be started the following morning
• Once prostaglandin gel or tablets are applied they cannot be removed (unlike the Cervidil insert) - so plan accordingly
• Resources for immediate delivery (cesarean) must be available before starting induction
• Misoprostol is cheaper and more stable than dinoprostone but is used off-label and is contraindicated after prior cesarean

• Pfenninger and Fowler's Procedures for Primary Care, 3rd ed. (Induction of Labor, Table 163-2)
• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice (Indicated Induction, p. 952)
• Textbook of Family Medicine 9e, p. 505