Induction of Labour

Induction of labour (IOL) is the artificial initiation of uterine contractions before their spontaneous onset, with the aim of achieving vaginal delivery after the period of viability. It is among the commonest planned obstetric interventions and a recurring NEET PG topic for its sharp recall facts — Bishop score cut-offs, misoprostol dosing, and absolute contraindications.

Definition and key terms

• Induction of labour: Stimulation of contractions in a woman not in labour, to deliver per vaginum.
• Augmentation of labour: Enhancement of contractions in a woman already in spontaneous labour but with inadequate progress (poor frequency/intensity).
• Cervical ripening: Softening, effacement and dilatation of an unfavourable cervix before or alongside induction, usually using prostaglandins or mechanical methods.
• Elective induction: No maternal/fetal indication except convenience or social reason (generally discouraged before 39 weeks).
• Indicated induction: A clear maternal or fetal benefit to ending the pregnancy.

High-yield: "Induction" = woman NOT in labour. "Augmentation" = woman ALREADY in labour. This distinction is a classic one-line MCQ trap.

Indications for induction

The principle is that continuation of pregnancy carries more risk to mother or fetus than delivery.

Maternal indications

• Pre-eclampsia, eclampsia, gestational/chronic hypertension
• Diabetes (pre-gestational and gestational, especially poorly controlled)
• Chronic renal disease, cardiac disease where prolongation is harmful
• Antepartum haemorrhage (e.g. controlled abruption with a stable mother and fetus)
• Chorioamnionitis / intrauterine infection
• Obstetric cholestasis (intrahepatic cholestasis of pregnancy) — usually 37–38 weeks

Fetal / fetoplacental indications

• Post-term pregnancy (≥41 completed weeks — the single most common indication worldwide)
• PROM / PPROM (prelabour rupture of membranes)
• Intrauterine growth restriction (IUGR) with reassuring or borderline surveillance
• Oligohydramnios
• Rh isoimmunisation / haemolytic disease
• Intrauterine fetal death (IUFD) — induction is offered for delivery
• Fetal congenital anomaly where delivery is planned

High-yield: Post-datism (≥41 weeks) is the commonest indication for induction. Beyond 41–42 weeks the risk of stillbirth, meconium aspiration and oligohydramnios rises sharply.

Contraindications

These mirror the contraindications to vaginal delivery — if vaginal birth is unsafe, induction is pointless or dangerous.

Absolute contraindications	Relative contraindications
Previous classical (vertical) caesarean or inverted-T uterine incision	One previous lower-segment caesarean (induction possible but cautious; misoprostol avoided)
Previous myomectomy entering the uterine cavity / hysterotomy	Grand multiparity
Placenta praevia / vasa praevia	Multiple gestation
Cord presentation / cord prolapse	Breech presentation
Transverse / oblique lie	Polyhydramnios (overdistension)
Active genital herpes infection	Maternal cardiac disease (select cases)
Invasive cervical carcinoma	Severe IUGR with abnormal Doppler
Cephalopelvic disproportion (CPD), contracted pelvis

High-yield: The two contraindications most repeated in NEET PG stems are prior classical caesarean section and placenta praevia. Also remember that PGE analogues (especially misoprostol) are contraindicated in any woman with a uterine scar because of the high uterine rupture risk.

The Bishop Score — the decision-maker

Before induction, the cervix is assessed to predict the likelihood of success. The Bishop score (modified Bishop / Calder modification) grades five parameters, each 0–3 (position and consistency are 0–2), maximum 13.

Parameter	0	1	2	3
Dilatation (cm)	Closed	1–2	3–4	≥5
Effacement (%)	0–30	40–50	60–70	≥80
Station (relative to ischial spines)	−3	−2	−1/0	+1/+2
Cervical consistency	Firm	Medium	Soft	—
Cervical position	Posterior	Mid	Anterior	—

Interpretation

• Bishop score ≥ 6 (some texts ≥ 8) = favourable ("ripe") cervix → proceed directly to amniotomy ± oxytocin; high chance of successful vaginal delivery.
• Bishop score < 6 = unfavourable cervix → requires cervical ripening first (prostaglandins or mechanical methods).

High-yield: A Bishop score ≥ 6 is the most quoted threshold for a "favourable" cervix and predicts successful induction. A score < 6 mandates ripening before oxytocin. Memorise the five components.

Mnemonic for Bishop components — "Dilation Can Easily Predict Success": Dilatation, Consistency, Effacement, Position, Station.

Methods of induction and cervical ripening

Methods fall into pharmacological and mechanical/surgical groups. Choice depends mainly on the Bishop score and the presence of a uterine scar.

Stepwise approach

Assess Bishop score → If <6: ripen cervix (PGE2 / misoprostol / Foley) → reassess → Once favourable (≥6) or already favourable: amniotomy (ARM) → start oxytocin infusion → titrate to adequate contractions → monitor with CTG → Deliver / reassess for failed induction.

1. Prostaglandins (pharmacological ripening)

Dinoprostone (PGE2) — preferred ripening agent where a scar is present or misoprostol is contraindicated.

• Forms: vaginal gel (0.5 mg), vaginal tablet (3 mg), or controlled-release vaginal insert/pessary (10 mg) releasing ~0.3 mg/hour over 12–24 h.
• Advantage: the slow-release insert can be removed promptly if hyperstimulation occurs.

Misoprostol (PGE1 analogue) — cheap, heat-stable, highly effective; widely used in India.

• Dose: 25 µg vaginally every 4–6 hours (oral 25–50 µg). Maximum commonly cited as up to ~6 doses / 24 h.
• Do not start oxytocin within ~4 hours of the last misoprostol dose (additive uterine stimulation → hyperstimulation).
• Contraindicated with any uterine scar / previous caesarean owing to rupture risk.

High-yield: The exam-favourite misoprostol cervical-ripening dose is 25 µg per vaginum 4–6 hourly. Higher doses raise tachysystole and uterine rupture risk. Misoprostol is the agent of choice for second-trimester IUFD and for induction where cost/storage matter, but is avoided with a prior caesarean scar.

Feature	Dinoprostone (PGE2)	Misoprostol (PGE1)
Cost / storage	Expensive, refrigeration	Cheap, heat-stable
Usual route	Vaginal gel/insert	Vaginal / oral
Ripening dose	Gel 0.5 mg; insert 10 mg	25 µg PV 4–6 hourly
Use with uterine scar	Relatively safer (still cautious)	Contraindicated
Reversibility	Insert removable	Not removable once given
Tachysystole risk	Lower	Higher

2. Mechanical methods

• Transcervical Foley catheter (balloon ~30–60 mL) placed through the internal os — exerts direct pressure and stimulates local prostaglandin release. Preferred ripening method in a woman with a previous caesarean (no pharmacological hyperstimulation).
• Double-balloon (Cook) catheter.
• Hygroscopic dilators (laminaria, synthetic Dilapan).
• Membrane sweeping / stripping — separating membranes from the lower segment at the internal os; releases endogenous prostaglandins; offered at term to promote spontaneous labour and reduce formal induction.

High-yield: In a woman with one previous LSCS needing ripening, the Foley balloon catheter is preferred over prostaglandins because it avoids pharmacological uterine hyperstimulation and rupture risk.

3. Surgical / pharmacological induction once cervix is favourable

• Amniotomy (ARM, artificial rupture of membranes): Done with a favourable cervix; releases prostaglandins, shortens labour. Risks: cord prolapse (high head), infection, vasa praevia bleeding. Always confirm engagement and exclude cord presentation first.
• Oxytocin infusion: Used after ARM, or for augmentation. Standard regimen — start low (e.g. 1–2 mU/min), increase every 30 minutes until 3–5 contractions in 10 minutes, each lasting ~40–60 s. Requires continuous CTG monitoring. Oxytocin's antidiuretic effect can cause water intoxication / hyponatraemia at high doses with hypotonic fluids.

High-yield: ARM + oxytocin is the standard induction sequence for a favourable cervix. Oxytocin is titrated to a target of 3–5 contractions per 10 minutes. Watch for hyperstimulation and water intoxication.

Failed induction

Definition (commonly used): Failure to achieve regular contractions and cervical change after an adequate trial — typically failure to enter active labour after ≥ 24 hours of oxytocin (after membrane rupture, where feasible). It is distinct from arrest of labour in the active phase.

• ACOG-type criterion: oxytocin for at least 12–18 hours after membrane rupture before declaring failed induction.
• Management of true failed induction (with intact viable fetus and no progress despite adequate stimulation) is usually caesarean section.

High-yield: Failed induction is generally diagnosed when the patient does not enter active labour despite ≥24 hours of induction / adequate oxytocin (with ruptured membranes). The usual next step is caesarean delivery.

Complications of induction

Complication	Notes / management
Uterine tachysystole / hyperstimulation	>5 contractions/10 min averaged over 30 min, ± fetal heart-rate changes. Stop/reduce oxytocin, remove PG insert, left lateral position, O₂, IV fluids, tocolysis (terbutaline)
Fetal distress	From hyperstimulation/cord compression; CTG monitoring is mandatory
Uterine rupture	Especially with prostaglandins on a scarred uterus — obstetric emergency
Cord prolapse	After ARM with unengaged/high head
Failed induction → caesarean	Increased CS rate, particularly with unfavourable cervix/nulliparity
Chorioamnionitis	Prolonged induction with ruptured membranes
Postpartum haemorrhage	Uterine atony after prolonged oxytocin exposure
Water intoxication / hyponatraemia	High-dose oxytocin + hypotonic fluids (oxytocin is structurally close to ADH)
Amniotic fluid embolism	Rare but recognised association

High-yield: Tachysystole = >5 contractions in 10 minutes (averaged over 30 min). First-line rescue tocolytic for iatrogenic hyperstimulation is subcutaneous/IV terbutaline. Remove the prostaglandin insert and stop oxytocin.

Special situations

• Previous one caesarean (TOLAC/VBAC): Spontaneous labour preferred. If induction needed, mechanical methods (Foley) are favoured; misoprostol is contraindicated; oxytocin/dinoprostone used cautiously with vigilant monitoring for scar rupture.
• PROM at term: Induction (commonly oxytocin) reduces chorioamnionitis vs expectant management.
• Intrauterine fetal death (IUFD): Misoprostol is the agent of choice (dose depends on gestational age — higher in second trimester, lower near term); mifepristone may precede it. No CTG needed (no live fetus), but watch for coagulopathy in prolonged retention.
• Post-term: Offer membrane sweep and induction by 41–42 weeks to reduce stillbirth.

Differentials / things often confused

• Induction vs Augmentation — see definitions above (the single commonest confusion).
• Failed induction vs arrest of labour — failed induction = never entered active phase; arrest = entered active phase then stopped progressing.
• Cervical ripening vs Induction — ripening prepares an unfavourable cervix; it may or may not itself trigger labour.
• Tachysystole vs normal active labour — normal active labour is 3–5 contractions/10 min; tachysystole is >5/10 min.

Recently asked / exam angle

NEET PG and INI-CET questions on this topic cluster around a few predictable stems:

• "Most common indication for induction?" → Post-term pregnancy (≥41 weeks).
• "Bishop score components / favourable cut-off?" → Five parameters; ≥6 favourable. Single-best-answer items frequently ask which parameter is NOT in the Bishop score (e.g. fetal weight, presentation — these are distractors).
• "Misoprostol dose for cervical ripening?" → 25 µg vaginally 4–6 hourly.
• "Contraindication to induction / to misoprostol?" → Previous classical CS, placenta praevia, transverse lie; misoprostol contraindicated with any uterine scar.
• "Drug for second-trimester IUFD / MTP induction?" → Misoprostol (± mifepristone).
• Scenario stems: A G2P1 with previous LSCS and unfavourable cervix needing delivery → answer is mechanical ripening (Foley), not prostaglandins. Tachysystole on oxytocin → stop oxytocin + terbutaline.
• Definition discrimination: Induction vs augmentation; favourable vs unfavourable cervix.

Rapid revision

1. Induction = woman not in labour; Augmentation = already in labour.
2. Commonest indication = post-term pregnancy (≥41 weeks).
3. Bishop score ≥6 = favourable → ARM + oxytocin; <6 = ripen first.
4. Bishop parameters: Dilatation, Effacement, Station, Consistency, Position (max 13).
5. Misoprostol ripening dose = 25 µg PV every 4–6 hours.
6. Misoprostol is contraindicated in any uterine scar / previous caesarean.
7. Foley balloon = preferred ripening method with a previous LSCS.
8. Absolute contraindications: classical CS, placenta praevia, transverse lie, cord prolapse, active genital herpes.
9. Oxytocin titrated to 3–5 contractions per 10 minutes; risk of water intoxication.
10. Tachysystole = >5 contractions/10 min; treat by stopping oxytocin + terbutaline.
11. Failed induction = no active labour after ≥24 h of adequate induction → caesarean.
12. Misoprostol (± mifepristone) is the agent of choice for second-trimester IUFD.