Obstetric Topic 25. Induction and augmentation of labor

I. Definitions and Indications

Definitions

• Induction of labor: artificial initiation of uterine contractions before spontaneous labor.
• Augmentation of labor: stimulation of spontaneous but inadequate contractions.
• Basic principle: induce when risks of continuing pregnancy ≥ risks of delivery.
• Prerequisites: correct gestational age, fetal presentation known, fetal status assessed, no vaginal-delivery contraindication, cesarean capability available.

Indications for Induction

• Post-term/late-term pregnancy.
• Preeclampsia, eclampsia, HELLP, gestational hypertension.
• Maternal disease: diabetes, renal/lung/heart disease when delivery is safer.
• PROM/PPROM according to gestational age and infection risk.
• Chorioamnionitis.
• Fetal: IUFD, IUGR/FGR, abnormal fetal testing/fetal jeopardy, severe fetal anomaly.
• Rh isoimmunization / hemolytic disease when delivery indicated.

Contraindications

• Contraindications to vaginal delivery: placenta previa, vasa previa, cord prolapse/presentation, invasive cervical cancer, active genital herpes.
• Mechanical obstruction: severe CPD/contracted pelvis, pelvic mass.
• Abnormal lie/presentation: transverse or persistent oblique lie, non-deliverable malpresentation.
• High uterine rupture risk: previous classical cesarean/T-incision, full-thickness uterine surgery, some myomectomies.
• Previous low-transverse cesarean is not an absolute contraindication, but prostaglandins are restricted and VBAC protocol is required.
• Acute fetal distress requiring immediate delivery → usually cesarean, not induction.

II. Bishop Score and Cervical Ripening

Bishop Score

• Purpose: pre-induction assessment of cervical favorability and chance of vaginal delivery.
• Parameters: cervical dilation, effacement/length, consistency, position, fetal head station.
• Favorable cervix: commonly ≥6; high success especially around ≥8-9.
• Unfavorable cervix: <6 → cervical ripening before induction.

Cervical Ripening Methods

• Prostaglandins: PGE2/dinoprostone or low-dose PGE1/misoprostol → cervical softening, effacement, contractions.
• Mechanical: Foley/balloon catheter → gentle cervical dilation; lower tachysystole risk than prostaglandins.
• Osmotic dilators/laminaria: selected cases.
• Membrane sweeping: digital separation of membranes from lower uterine segment; may trigger endogenous prostaglandins.
• Avoid misoprostol for term induction after previous cesarean/major uterine scar because of uterine rupture risk.

III. Induction and Augmentation Procedures

Induction with Favorable Cervix

1. Confirm cephalic presentation, engaged/stable head, reassuring fetal status.
2. Amniotomy: artificial rupture of membranes; check immediately for cord prolapse and amniotic fluid color.
3. Oxytocin IV infusion: low-dose, titrated to adequate contractions.
4. Continuous monitoring: uterine activity, fetal heart rate, maternal pulse/BP.

Augmentation of Labor

• Indication: spontaneous labor with inadequate contractions and slow dilation/descent.
• Before augmentation: rule out CPD, malposition, malpresentation, fetal distress and uterine rupture risk.
• Methods: amniotomy if safe; oxytocin IV infusion carefully titrated.
• Use minimum oxytocin dose needed for adequate contractions.

IV. Complications and Failed Induction

Complications

• Uterine tachysystole/hyperstimulation → fetal hypoxia/distress.
• Uterine rupture: especially scarred uterus or excessive stimulation.
• Cord prolapse after amniotomy, especially high/unengaged presenting part.
• Infection risk after prolonged rupture of membranes.
• Oxytocin water intoxication/hyponatremia: rare, with high dose/prolonged infusion.
• Failed induction → cesarean or reassessment/rest/further induction attempt if safe.

Management of Tachysystole

1. Stop/reduce oxytocin; remove prostaglandin insert if possible.
2. Maternal left lateral position and IV fluids.
3. Continuous CTG; treat fetal heart rate abnormality urgently.
4. Tocolysis (e.g. terbutaline) if persistent contractions with fetal compromise.